I've had something similar about a year back when using 3 Apple silicon Macs. I submitted an internal bug report which was reproducible with below steps. Bug was fixed. I've seen it again a few times since, but can't find the steps to reproduce it. So, chances of a fix are slim until it can be reproduced.
1. Launch LrC 2. Double click a grid view image to display in loupe view 3. Switch to the Develop module 4. Switch back to the Library module 5. Double click on Library loupe image to switch back to grid view
Actual Result: Green flashes occur on grey background.