You can see Steam Client logs here:
$ cat /tmp/dumps/`id -un`_stdout.txt
Yes, I took a look at it, and couldn't see anything relevant.
Here it is in case anyone wants to take a look: https://gist.github.com/Anden/d14d016175bc0cabc7cf
Tried reinstalling steam entirely, and that fixed the issue, so I guess something with the old install must have been broken.
Nothing extracted yet.
The steam overlay is not working for Kerbal Space Program, but is working for other games.
Uninstalling and reinstalling KSP did not help.
/tmp/gameoverlayui.log is not even created.
Nothing is indicating a problem on the steam command line output, in dmesg or in the system logs (journalctl).
The overlay starts working if I set SteamGameId to another games ID, but then I obviously have the info (achievements, news, etc.) from the other game.