After upgrading from 8.1 to 8.5.1 our advanced alerts relating to memory used were corrupted. Alerts with statements like
"Percent Memory Used is greater than 95"
were changed to
"* greater than 95"
After opening the alert in Alert manager and trying to save it again, it would generate an error about the condition being invalid.
I just discovered today that we had the same problem - and I didn't know about it until now, we did the upgrade two weeks ago.