Ok, tested with 1.6.34 as well, still works, so it's something on your end.
Test these, in ascending order of gravity of change:
-
Reset match layout in preferences (top group of buttons)
- Exit Forge, move all files out of C:\Users\<YOU>\AppData\Roaming\Forge\preferences to somewhere safe and retry
- Download a new archive of Forge, unzip to someplace else, try from there
You can also post your Forge.log (C:\Users\<YOU>\AppData\Roaming\Forge) after it happened again (I doubt it'll register/reflect this though)
Not sure a screenshot right when/after it happens will contain more clues..
Fingers crossed!
K.