Currently, there are two persistent problems (Windows 10 x64, gtk3.22 client):
Firstly, the tile info box that appears when middle-clicking the map has no background. The text is there, but it's hard to discern in front of the terrain.
Secondly, the client simply crashes occasionally when trying to drag an item in a city's worklist. This doesn't always happen and I haven't been able to figure out, when exactly it happens, but it's a thing that's happening. I'll try to find out the exact circumstances triggering this.
EDIT: Also, the color pickers (I presume) for Client Settings → Graphics → "Color to highlight your player/user name" don't work and cause a crash.
EDIT2: Also, the vote bar takes up half the screen