Actions (edit, rollback , etc.) that are performed directly.
If you attempt to post an edit form and bypass the notice (through a gadget?) or you attempt to perform some other action directly that has no page (like rollback), the block notice page the user gets is not logged.
The Action class will throw a PermissionsError or a UserBlockedError when that happens, it should be tracked (if it is a block that is the cause of the error).