Today I am having the same issue. I removed the container, removed the FileZilla appdata folder so it would be a clean install. I tried starting up the docker and it gave me a few errors:
[s6-init] making user provided files available at /var/run/s6/etc...exited 0.
[s6-init] ensuring user provided files have correct perms...exited 0.
[fix-attrs.d] applying ownership & permissions fixes...
[fix-attrs.d] done.
[cont-init.d] executing container initialization scripts...
[cont-init.d] 00-app-niceness.sh: executing...
[cont-init.d] 00-app-niceness.sh: exited 0.
[cont-init.d] 00-app-script.sh: executing...
[cont-init.d] 00-app-script.sh: exited 0.
[cont-init.d] 00-app-user-map.sh: executing...
[cont-init.d] 00-app-user-map.sh: exited 0.
[cont-init.d] 00-clean-logmonitor-states.sh: executing...
[cont-init.d] 00-clean-logmonitor-states.sh: exited 0.
[cont-init.d] 00-clean-tmp-dir.sh: executing...
[cont-init.d] 00-clean-tmp-dir.sh: exited 0.
[cont-init.d] 00-set-app-deps.sh: executing...
[cont-init.d] 00-set-app-deps.sh: exited 0.
[cont-init.d] 00-set-home.sh: executing...
[cont-init.d] 00-set-home.sh: exited 0.
[cont-init.d] 00-take-config-ownership.sh: executing...
[cont-init.d] 00-take-config-ownership.sh: exited 0.
[cont-init.d] 00-xdg-runtime-dir.sh: executing...
[cont-init.d] 00-xdg-runtime-dir.sh: exited 0.
[cont-init.d] 10-certs.sh: executing...
[cont-init.d] 10-certs.sh: exited 0.
[cont-init.d] 10-cjk-font.sh: executing...
[cont-init.d] 10-cjk-font.sh: exited 0.
[cont-init.d] 10-nginx.sh: executing...
[cont-init.d] 10-nginx.sh: exited 0.
[cont-init.d] 10-vnc-password.sh: executing...
[cont-init.d] 10-vnc-password.sh: exited 0.
[cont-init.d] 10-web-index.sh: executing...
[cont-init.d] 10-web-index.sh: exited 0.
[cont-init.d] filezilla.sh: executing...
[cont-init.d] filezilla.sh: generating machine-id...
'/defaults/filezilla.xml' -> '/config/xdg/config/filezilla/filezilla.xml'
[cont-init.d] filezilla.sh: exited 0.
[cont-init.d] done.
[services.d] starting services
[services.d] starting s6-fdholderd...
[services.d] starting nginx...
[services.d] starting certsmonitor...
[nginx] starting...
[services.d] starting xvfb...
[certsmonitor] disabling service: secure connection not enabled.
[xvfb] starting...
[services.d] starting statusmonitor...
[services.d] starting x11vnc...
[services.d] starting logmonitor...
[x11vnc] starting...
[services.d] starting openbox...
24/02/2020 15:33:43 passing arg to libvncserver: -rfbport
24/02/2020 15:33:43 passing arg to libvncserver: 5900
24/02/2020 15:33:43 passing arg to libvncserver: -rfbportv6
24/02/2020 15:33:43 passing arg to libvncserver: -1
24/02/2020 15:33:43 passing arg to libvncserver: -httpportv6
24/02/2020 15:33:43 passing arg to libvncserver: -1
24/02/2020 15:33:43 passing arg to libvncserver: -desktop
24/02/2020 15:33:43 passing arg to libvncserver: FileZilla
24/02/2020 15:33:43 x11vnc version: 0.9.14 lastmod: 2015-11-14 pid: 783
[statusmonitor] no file to monitor: disabling service...
[logmonitor] no file to monitor: disabling service...
24/02/2020 15:33:43 Using X display :0
24/02/2020 15:33:43 rootwin: 0x43 reswin: 0x200001 dpy: 0x566f79e0
24/02/2020 15:33:43
24/02/2020 15:33:43 ------------------ USEFUL INFORMATION ------------------
[openbox] starting...
24/02/2020 15:33:43 X DAMAGE available on display, using it for polling hints.
24/02/2020 15:33:43 To disable this behavior use: '-noxdamage'
24/02/2020 15:33:43
24/02/2020 15:33:43 Most compositing window managers like 'compiz' or 'beryl'
24/02/2020 15:33:43 cause X DAMAGE to fail, and so you may not see any screen
24/02/2020 15:33:43 updates via VNC. Either disable 'compiz' (recommended) or
24/02/2020 15:33:43 supply the x11vnc '-noxdamage' command line option.
24/02/2020 15:33:43 X COMPOSITE available on display, using it for window polling.
24/02/2020 15:33:43 To disable this behavior use: '-noxcomposite'
24/02/2020 15:33:43
24/02/2020 15:33:43 Wireframing: -wireframe mode is in effect for window moves.
24/02/2020 15:33:43 If this yields undesired behavior (poor response, painting
24/02/2020 15:33:43 errors, etc) it may be disabled:
24/02/2020 15:33:43 - use '-nowf' to disable wireframing completely.
24/02/2020 15:33:43 - use '-nowcr' to disable the Copy Rectangle after the
24/02/2020 15:33:43 moved window is released in the new position.
24/02/2020 15:33:43 Also see the -help entry for tuning parameters.
24/02/2020 15:33:43 You can press 3 Alt_L's (Left "Alt" key) in a row to
24/02/2020 15:33:43 repaint the screen, also see the -fixscreen option for
24/02/2020 15:33:43 periodic repaints.
24/02/2020 15:33:43 GrabServer control via XTEST.
24/02/2020 15:33:43
24/02/2020 15:33:43 Scroll Detection: -scrollcopyrect mode is in effect to
24/02/2020 15:33:43 use RECORD extension to try to detect scrolling windows
24/02/2020 15:33:43 (induced by either user keystroke or mouse input).
24/02/2020 15:33:43 If this yields undesired behavior (poor response, painting
24/02/2020 15:33:43 errors, etc) it may be disabled via: '-noscr'
24/02/2020 15:33:43 Also see the -help entry for tuning parameters.
24/02/2020 15:33:43 You can press 3 Alt_L's (Left "Alt" key) in a row to
24/02/2020 15:33:43 repaint the screen, also see the -fixscreen option for
24/02/2020 15:33:43 periodic repaints.
24/02/2020 15:33:43
24/02/2020 15:33:43 XKEYBOARD: number of keysyms per keycode 7 is greater
24/02/2020 15:33:43 than 4 and 51 keysyms are mapped above 4.
24/02/2020 15:33:43 Automatically switching to -xkb mode.
24/02/2020 15:33:43 If this makes the key mapping worse you can
24/02/2020 15:33:43 disable it with the "-noxkb" option.
24/02/2020 15:33:43 Also, remember "-remap DEAD" for accenting characters.
24/02/2020 15:33:43
24/02/2020 15:33:43 X FBPM extension not supported.
Xlib: extension "DPMS" missing on display ":0".
24/02/2020 15:33:43 X display is not capable of DPMS.
24/02/2020 15:33:43 --------------------------------------------------------
24/02/2020 15:33:43
24/02/2020 15:33:43 Default visual ID: 0x21
24/02/2020 15:33:43 Read initial data from X display into framebuffer.
24/02/2020 15:33:43 initialize_screen: fb_depth/fb_bpp/fb_Bpl 24/32/5120
24/02/2020 15:33:43
24/02/2020 15:33:43 X display :0 is 32bpp depth=24 true color
24/02/2020 15:33:43
24/02/2020 15:33:43 Listening for VNC connections on TCP port 5900
24/02/2020 15:33:43
24/02/2020 15:33:43 Xinerama is present and active (e.g. multi-head).
24/02/2020 15:33:43 Xinerama: number of sub-screens: 1
24/02/2020 15:33:43 Xinerama: no blackouts needed (only one sub-screen)
24/02/2020 15:33:43
24/02/2020 15:33:43 fb read rate: 1384 MB/sec
24/02/2020 15:33:43 fast read: reset -wait ms to: 10
24/02/2020 15:33:43 fast read: reset -defer ms to: 10
24/02/2020 15:33:43 The X server says there are 10 mouse buttons.
24/02/2020 15:33:43 screen setup finished.
24/02/2020 15:33:43
The VNC desktop is: 679299f9f350:0
0
******************************************************************************
Have you tried the x11vnc '-ncache' VNC client-side pixel caching feature yet?
The scheme stores pixel data offscreen on the VNC viewer side for faster
retrieval. It should work with any VNC viewer. Try it by running:
x11vnc -ncache 10 ...
One can also add -ncache_cr for smooth 'copyrect' window motion.
More info: http://www.karlrunge.com/x11vnc/faq.html#faq-client-caching
[services.d] starting app...
[app] starting FileZilla...
[services.d] done.
Reading locale option from /config/xdg/config/filezilla/filezilla.xml
** (filezilla:847): WARNING **: 15:33:45.794: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.794: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.799: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.799: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.835: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.835: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.840: invalid source position for vertical gradient
** (filezilla:847): WARNING **: 15:33:45.840: invalid source position for vertical gradient
24/02/2020 15:33:49 Got connection from client 127.0.0.1
24/02/2020 15:33:49 other clients:
24/02/2020 15:33:49 Got 'ws' WebSockets handshake
24/02/2020 15:33:49 Got protocol: binary
24/02/2020 15:33:49 - webSocketsHandshake: using binary/raw encoding
24/02/2020 15:33:49 - WebSockets client version hybi-13
24/02/2020 15:33:49 Disabled X server key autorepeat.
24/02/2020 15:33:49 to force back on run: 'xset r on' (3 times)
24/02/2020 15:33:49 incr accepted_client=1 for 127.0.0.1:57588 sock=10
24/02/2020 15:33:49 webSocketsDecodeHybi: got frame without mask
24/02/2020 15:33:49 rfbProcessClientProtocolVersion: read: I/O error
24/02/2020 15:33:49 client_count: 0
24/02/2020 15:33:49 Restored X server key autorepeat to: 1
24/02/2020 15:33:49 Client 127.0.0.1 gone
24/02/2020 15:33:49 Statistics events Transmit/ RawEquiv ( saved)
24/02/2020 15:33:49 TOTALS : 0 | 0/ 0 ( 0.0%)
24/02/2020 15:33:49 Statistics events Received/ RawEquiv ( saved)
24/02/2020 15:33:49 TOTALS : 0 | 0/ 0 ( 0.0%)
24/02/2020 15:33:55 Got connection from client 127.0.0.1
24/02/2020 15:33:55 other clients:
24/02/2020 15:33:55 Got 'ws' WebSockets handshake
24/02/2020 15:33:55 Got protocol: binary
24/02/2020 15:33:55 - webSocketsHandshake: using binary/raw encoding
24/02/2020 15:33:55 - WebSockets client version hybi-13
24/02/2020 15:33:55 Disabled X server key autorepeat.
24/02/2020 15:33:55 to force back on run: 'xset r on' (3 times)
24/02/2020 15:33:55 incr accepted_client=2 for 127.0.0.1:57594 sock=10
24/02/2020 15:33:55 webSocketsDecodeHybi: got frame without mask
24/02/2020 15:33:55 rfbProcessClientProtocolVersion: read: I/O error
24/02/2020 15:33:55 client_count: 0
24/02/2020 15:33:55 Restored X server key autorepeat to: 1
24/02/2020 15:33:55 Client 127.0.0.1 gone
24/02/2020 15:33:55 Statistics events Transmit/ RawEquiv ( saved)
24/02/2020 15:33:55 TOTALS : 0 | 0/ 0 ( 0.0%)
24/02/2020 15:33:55 Statistics events Received/ RawEquiv ( saved)
24/02/2020 15:33:55 TOTALS : 0 | 0/ 0 ( 0.0%)
There are also a few redmarked error lines in there:
24/02/2020 15:33:49 rfbProcessClientProtocolVersion: read: I/O error
filezilla: Fatal IO error 22 (Invalid argument) on X server :0.