Brush tool not working on layer Masks

The brush tool is not working when painting on a layer mask. Opacity, blend mode, brush setting, color (black/white) all normal. I either have to change tools, change layers or make some other change to get it to start working again. Totally random which “fix” will get the tool working again.

Also, when in Quick mask mode, a black or white brush will paint white. Again, all settings “normal”.

Running 28.01 Beta. 
M4 Max 
OS Golden State v. 27.2