The carpenter building refuses to spawn when I use the blueprint. After I creatively spawned the building and the carpenter himself, the blueprints started working. I'm using the farming valley pack v:0.6.9 using harvest festival 5.22.

This makes zero sense whatsoever and doesn't happen to me. Also FYI that pack has inventory tweaks which is known to be rather buggy in the current versions.

I created a server for the mod which resolved but created more problems. The carpenter problem went away, however, I was having a bug where I could see the items I was receiving but touching my inventory deleted the item. This is related to inventory tweaks I would think. This was also only client side as my friend had no problems. The root of the problem here was Inventory Tweaks I belive as you mentioned. I was having other problems but are unrelated.