Photoshop: Masking changes not updating

I have the latest version of adobe photoshop, 21.2, and my computer/operating system is catalina Mac OS...  10.15.5...  since downloading the latest photoshop version, when i'm working with layer masks, when i fill or brush within the mask, the real time effects do not show.  They are there because i can see them be painted onto the mask and if i afterwards toggle the layer visibility, they eventually show, so it is a real time rendering issue.  The layer mask is on the top layer, layer is not locked, brush mode is normal and opacity and flow are both 100%... so that rules out the conventional troubleshootings and as i said, if i toggle the layers, they eventually show the effect showing it was there, just not showing it.  Please advise adobe.