This is an issue @walkjivefly has mentioned before, and now I'm starting to experience it with increasing regularity.
The issue is that the SYS daemon, while running inside a docker container, seems to get out of sync with the blockchain quite easily/frequently. I think it happens more frequently if the host system is under heavy load.
Notably, @walkjivefly has noticed it never happens when the SYS daemon is running outside of a docker container. It only seems to happen in our EXR ENV, where SYS daemon runs inside a docker container. This suggests the issue is related to the way SYS daemon is being run in a docker container in our EXR ENV.
The importance of this issue has recently increased significantly as we prepare to provide reliably indexed SYS NEVM data via XQuery.