Thanks for reaching out. I’ll need more information so that I can help you with this issue.
Could you please share the location of the original/source images? Are they on the internal drive or an external drive? Are you using Solid State Drives (SSD) or HDD? Does this happen when editing images with a specific set or collection? Where is the catalog stored? Is it on an internal drive or an external drive?
Are you using multiple monitors? Does this behavior appear after a series of steps or in any screen mode like fullscreen?
Do you use any other resource-intensive application that might be behaving oddly?
Thanks. It's magically working today. I am totally baffled. No reboot. LR still running from yesterday. I just picked up with my edits where I left off and the problem is gone. I will make note of the restart procedure if it happens again.