It looks like there are still/new issues with the Barotrauma docker (or rather, with the dedicated server.)
Running from a fresh install results:
---Checking if UID: 99 matches user---
---Checking if GID: 100 matches user---
---Setting umask to 000---
---Checking for optional scripts---
---No optional script found, continuing---
---Starting...---
---Update SteamCMD---
Redirecting stderr to '/serverdata/Steam/logs/stderr.txt'
[ 0%] Checking for available updates...
[----] Verifying installation...
Steam Console Client (c) Valve Corporation
-- type 'quit' to exit --
Loading Steam API...OK.
Connecting anonymously to Steam Public...Logged in OK
Waiting for user info...OK
---Update Server---
Redirecting stderr to '/serverdata/Steam/logs/stderr.txt'
[ 0%] Checking for available updates...
[----] Verifying installation...
Steam Console Client (c) Valve Corporation
-- type 'quit' to exit --
Loading Steam API...OK.
Connecting anonymously to Steam Public...Logged in OK
Waiting for user info...OK
Success! App '1026340' already up to date.
---Prepare Server---
---Checking for 'serversettings.xml'---
---'serversettings.xml' found...
---Checking if everything is in place---
---Correcting errors---
cp: cannot stat '/serverdata/serverfiles/linux64/steamclient.so': No such file or directory
---Something went wrong, can't copy 'steamclient.so' putting server into sleep mode---
I'm not very confident on linux cli, but I did some basic troubleshooting, here's my result. Hopefully its helpful.
Checking the /serverdata/serverfiles/ directory reveals that no linux64 subdir exists, but there is a steamclient.so within serverfiles.
If I create the linux64 subdir and copy steamclient.so into it, after a restart of the docker this results that the server "runs" but apparently fails at some point
---Checking if UID: 99 matches user---
usermod: no changes
---Checking if GID: 100 matches user---
usermod: no changes
---Setting umask to 000---
---Checking for optional scripts---
---No optional script found, continuing---
---Starting...---
---Update SteamCMD---
Redirecting stderr to '/serverdata/Steam/logs/stderr.txt'
[ 0%] Checking for available updates...
[----] Verifying installation...
Steam Console Client (c) Valve Corporation
-- type 'quit' to exit --
Loading Steam API...OK.
Connecting anonymously to Steam Public...Logged in OK
Waiting for user info...OK
---Update Server---
Redirecting stderr to '/serverdata/Steam/logs/stderr.txt'
[ 0%] Checking for available updates...
[----] Verifying installation...
Steam Console Client (c) Valve Corporation
-- type 'quit' to exit --
Loading Steam API...OK.
Connecting anonymously to Steam Public...Logged in OK
Waiting for user info...OK
Success! App '1026340' already up to date.
---Prepare Server---
---Checking for 'serversettings.xml'---
---'serversettings.xml' found...
---Checking if everything is in place---
---Correcting errors---
---Errors corrected---
---Checking for old logs---
---Server ready---
---Start Server---
Barotrauma Dedicated Server 0.10.4.0 (ReleaseLinux, branch release, revision 965c31410a)
Loading game settings
Loading MD5 hash cache
Initializing SteamManager
Initializing GameAnalytics
Initializing GameScreen
�[?1h�=�[6n�[39;49m�[37mLoaded languages: English, German, French, Russian, Polish, Brazilian Portuguese, Castilian Spanish, Latinamerican Spanish, Simplified Chinese, Traditional Chinese, Japanese, Turkish, Korean
�[39;49m�[30m�[6n �[12;1H�[11;1H�[39;49m�[37m�[6ndlopen failed trying to load:
steamclient.so
with error:
steamclient.so: cannot open shared object file: No such file or directory
[S_API] SteamAPI_Init(): Loaded '/serverdata/.steam/sdk64/steamclient.so' OK. (First tried local 'steamclient.so')
�[39;49m�[37mSelected sub: Azimuth
�[39;49m�[37mSelected shuttle: Hemulen
�[39;49m�[32m[9/14/2020 10:19:36 PM]
Starting the server...
�[39;49m�[32m[9/14/2020 10:19:36 PM]
Using Lidgren networking. Manual port forwarding may be required. If players cannot connect to the server, you may want to use the in-game hosting menu (which uses SteamP2P networking and does not require port forwarding).
�[39;49m�[31mCoroutine Barotrauma.Networking.GameServer+<StartServer>d__47 threw an exception: InitGameServer returned false (0,31004,27035,27036,2,"1.0.0.0")
at Steamworks.SteamServer.Init(AppId appid, SteamServerInit init, Boolean asyncCallbacks) in /home/joonas/Barotrauma/Libraries/Facepunch.Steamworks/SteamServer.cs:line 94
at Barotrauma.Steam.SteamManager.CreateServer(GameServer server, Boolean isPublic) in /home/joonas/Barotrauma/Barotrauma/BarotraumaServer/ServerSource/Networking/SteamManager.cs:line 26
at Barotrauma.Networking.GameServer.StartServer(Boolean isPublic)+MoveNext() in /home/joonas/Barotrauma/Barotrauma/BarotraumaServer/ServerSource/Networking/GameServer.cs:line 195
at Barotrauma.CoroutineManager.IsDone(CoroutineHandle handle) in /home/joonas/Barotrauma/Barotrauma/BarotraumaShared/SharedSource/CoroutineManager.cs:line 212
�[39;49m�[30m�[6n �[24;1H�[23;1H�[39;49m�[37m�[6n
This section appears particularly relevant.
Googling the line I've colored red leads me here:
https://github.com/Regalis11/Barotrauma/issues/2310
This is somewhat over my head, but it looks like the current server installed via steamcmd requires significant manual intervention in the form of creating several symlinks to a specific (or just more up to date?) version of steamclient.so in order for the DS to run correctly. Again, out of my depth.