AX2012 change based alerts stop working

I am having problems with change based alerts in AX2012. They initially work when I set them up, and they work for a few weeks, then they stop working.

I can’t see any reason why this happens. The batch job for processing the alerts is still running every minute, but alerts do not get generated.

Often I can edit the alert rules and just change the user ID that gets notified and the alert will start working again, but this does not always work and I have to recreate the alert from scratch.

Sometimes I can see the alerts appear in the EventCUD table, and I can see them being processed by refreshing the table repeatedly, however once the records have disappeared from EventCUD they don’t appear in the EventInbox table.

If anyone has any clue as to why this happens I would really appreciate an answer as it is extremely frustrating for our customer who relies on the alerts to notify users when certain actions need to be taken.