I am making datapack that creates new block called workbench. There is a function that happends when item frame cannot detect barrel on its position. It will kill item displays that have item with CustomModelData and will insert new nbt data to barrel item with specific name that dropped from the broken barrel. This happends normaly in creative mode or when I instantly break the barrel, but the longer I'm breking the barrel, the longer drop delay is. There is a screen recording and zip file of my datapack in the attachments. There are some unused files in the datapack, please pay them no mind. 

I also forgot to mention, when i was trying to debug it, it worked normaly when I removed part of the function where there was replacing item in the barrel. There were 27 parts of the functions (commented by "Slot 0", "Slot 1"...) which were summoning new item and inserting data from barrel into it and then replacing item in specific slot in the barrel with air. When I removed them, block delay was normal. Here is also the resourcepack if there is any need for it. If it is not a bug, please give me a tip how to fix it.

Resource Pack.zip

REC.mp4Datapack.zip