This seems to be happening too many times to be considered as isolated instances. PG doesn't seem to have any other response other than update to build 146. I looked up specs. on El Capitan and Sierra and Sierra takes up less memory so it would seem that is not the cause.
Janice & Bud, I am leery about running Dr. Cleaner memory manager, there are too many complaints.
In performance I rarely look at the computer screen so I will put up with the annoyance but it should be corrected.