Jfyi, I have a similar issue with elasticsearch:
https://community.zammad.org/t/elasticsearch-forgets-results-from-attachments-over-time/
Maybe the underlaying problem is the same.
Anyway, yes, although not a real solution cron does help. 
Jfyi, I have a similar issue with elasticsearch:
https://community.zammad.org/t/elasticsearch-forgets-results-from-attachments-over-time/
Maybe the underlaying problem is the same.
Anyway, yes, although not a real solution cron does help.