The block displays were 2 black carpets, and one stone button. As stated, the armour stand was copied and pasted over but not them, So include entities was on both since the armour stand did, however the displays didn't.
Since i wrote that, I've tried it again and the problem seems to be that the displays have very weird hitboxes.
Normally this doesn't really matter and if you NEED the autocomplete you can just take a comparator output into another command block
However it is still annoying