on week old unraid install I've had the same problem:
1 crushftp10 already running with port 443 configured as HTTPS
2 installed MyServer access and it shows error code 500 (in settings\Management access it uses the same port:443)
I was looking for the solution and found this post.
Some time later, after restarting Unraid I couldn't start crushftp (error: port 443 in use), but code 500 disappeard.
I have changed HTTPS port for crushftp10 and everything work fine (so far).