Notifications Stops joining in the cutom table

We have added a custom field to Notifications many months ago and it has worked fine.  Recently, at seemingly random times, we get 500 errors now and the cause is that the query has our custom field in it but SugarCRM isnt adding in the JOIN for the notifications_cstm table so I get a MySQL error 'Field notifications_cstm.hidden_c does not exist.  But it does and the problem is really that the query has no JOIN to the custom table.

I do a QRR and all is well again. 

But now it is happening several times an hour.  Does anyone have any ideas?