sometimes if i merge the item gone, i don"t know where is goes

when i combine items and suddenly i experience a bug then my item disappear.

when i try to merge the items, suddenly the item disappear and i cant seem to make it appear again...

When merging instead of actually merging two of the things of a kind both disappear

the items appear and when I put them to merge it's as if they weren't there

The items gets disappearing while merging for many times