I got these messages in the error log of a SQL Server instance:

SQL Server has encountered 1 occurrence(s) of cachestore flush for the 'Bound Trees' cachestore (part of plan cache) due to some database maintenance or reconfigure operations.
SQL Server has encountered 1 occurrence(s) of cachestore flush for the 'SQL Plans' cachestore (part of plan cache) due to some database maintenance or reconfigure operations.
SQL Server has encountered 1 occurrence(s) of cachestore flush for the 'Object Plans' cachestore (part of plan cache) due to some database maintenance or reconfigure operations.

I also saw messages about starting a certain database, even though the instance itself remained running. This struck me as odd.

Turns out AutoClose was enabled on those databases, generating the errors above. Best practices recommend to turn off AutoClose as this has a negative impact on performance due to the database needing to be remounted when a process tries to access it.