Minecraft Addon items disappearing in inventory after some time.

I have no idea why the addon items are suddenly disappearing from the survival and creative inventory after a couple hours, days, or month. This is a frustrating problem that I face and there are few fixes online which does not help at all or they are different from what I am experiencing. Is there a good fix for this? Inorder to prevent addon items from suddenly disappearing? I did not even mess with the packs in the Files and yet, all of the addon items can suddenly disappear. There is also one instance in our server where I have the items from the addon but the other player's addon items disappeared without any trace. BTW, This is Minecraft PE Bedrock.