Since the update to version 1.38 of the Linux dedicated server, every client attempting to connect immediately receives a "You were kicked off the game" error. This happens regardless of mods (vanilla's affected), server configuration, BattlEye, etc.
The cause appears to be a broken steamclient.so, which is linked against various desktop-specific dynamic libraries not usually present on a dedicated Linux server (see ldd_steamclient.so_1.38.txt). This is a regression, since the version 1.36 steamclient.so didn't have these dependencies (see ldd_steamclient.so_1.36.txt).
The server spits out the following error message, but starts anyway:
[S_API FAIL] SteamAPI_Init() failed; SteamAPI_IsSteamRunning() failed.
dlopen failed trying to load:
steamclient.so
with error:
libX11.so.6: cannot open shared object file: No such file or directory
[S_API FAIL] SteamAPI_Init() failed; unable to locate a running instance of Steam, or a local steamclient.so.
Players attempting to connect will be silently kicked off:
19:38:22 Player Actium connecting.
19:38:24 Player Actium connected (id=12345678901234567).
19:38:24 Player Actium disconnected. {F25443} {F25444} {F25445}