Images not showing in lightroom develop panel on mac

System:

Lightroom Classic 15.3.1 running on Mac mini M4 Pro 48GB 650GB spare storage.
Catalogue is on the internal Mac mini SSD.

Problems:

This problem occurs frequently:
Open up LRC, Edit three or four images in Develop module. Proceed to next image, but the image in the Develop module doesn’t change, or there is a grey panel. 
Shut down LRC - Writing Metadata changes into XMP…sticks at 29% and makes no further progress. So I have to force close LRC. I have tried disabling GPU etc.

Any suggestions please?

Thanks

Richard