ANOTHER UPDATE
I just tried setting up a TU server in a fresh new Xubuntu 16.04 64bit VM and still got the same error as mentioned above. Any ideas on what is different compared to old builds of the dedicated server?
Third Update
So I’ve recently started experimenting with the DS again. And to put it simply, the issue seems to lie in the fact that the steamclient.so I used was meant for 32-bit software only. So hence I did not properly copy the file from TU’s linux64 folder (even though the guide tells us to do so).
But because I finally fixed that issue, my Docker container finally works. It is available here: https://hub.docker.com/r/zennoe/tower-unite/
(mods feel free to lock this thread)