When using a deployer (may only work with wind mill haven't try anything else) if you put the item into the deployer hand and have an empty chest attached to the entire contraption, it seems to dupe the block in it's hand.
Please see video for example:
https://youtu.be/b0xXpFhEW8E

Aight, found the issue. Turns out having create inside an ftb claim chunk causing create to break in a few way. One being this dupe exploit, another being the portable storage interface breaking not taking items out after the first time and just being stuck connected.
Please see video demonstrating what I've found and hopefully helps you to reproduce it yourself
https://youtu.be/9a6ooSFC4N0

Was an architectury bug, fixed in 2.0.4c (when it releases) 3c4c9d8