Over the past couple hours, the forum theme changes on it’s own. Is Discourse working on something? I use the light theme and its gone back and forth between light and gray.
I dont have this issue.. Maybe because im using “Dark Endeavour” theme?
I had this happening with Endeavour Dark now it is a bit more back to normal but I will stick with “Horizon/Horizon Dark” now.
No changes for me. The theme looks like it always looks. 
was only me try to understand how discourse theming works, and its.. somehow unclear that it will show public if you use preview..
I had the same issue. The dark theme I was using all of a sudden didnt work anymore. Lokked terrible, with a log of gray and little contrast. pretty much like your screenshot.
I had to select Horizon / Horizon Dark to get back to a dark theme.
Should all be back to normal..