Crossbow Item set bug?

Hello there!

I've encountered a strange problem on my Tactician.
I did a map and after entering back to the hideout i had a strange sound and my item set 2 crossbow became unusable by my character("You cannot use this item. Its stats will be ignored"). I checked everything from the passive tree to the attributes but i can't figure out how did it become unusable all of a sudden. Anyone got any ideas?