Behaviour packs stop working

We have uploaded a behaviour pack with custom villager trades and a custom mob to our realm. the behavior pack works fine initially but randomly stops working 

 

When the behaviour pack stops working i download a copy of the realm and find the behavior pack files are missing from the world files and i have to add them in again and upload to the realm again.

Can not re create it on purpose. Sometimes the behavior packs work for a few hours, sometimes a day and sometimes a few days