Disappearing items problems

Hello guys! I have a small problem that I'll try to explain here.

I created an utility block that allows to input items, and when you click on the "refine" button, another item appears in an output slot. Example : input a diamond, get a coal.

The problem is that I CANNOT COLLECT THE OUTPUT ITEM. Each time I try, the item vanishes, either giving back my diamond, either giving back nothing. When I try to shift-click to place immediately the item in my inventory, it works, but when I close the GUI, the item disappears, effectively destroying the input item. I also tried to create a "collect" button that automatically places the output in my inventory, but when I close the GUI, everything vanishes... and I really need to fix this bug as this block is the only way to access some items in my mod.

Here is the link to my mod : https://mcreator.net/modification/50924/mineral-galore-tons-new-gems-and-metals

The bugged block is the Ore Dissocier. Can someone help me quickly please, I want to fix that bug for the next update!