Anytime the item is thrown from the offhand, the mod thinks it is being thrown from the main hand. Because of this the item in the main hand slot is deleted and thrown as a hat and is now forever a hat.

In the video I use an empty hand as you can always reproduce it making a new one. With an item in the hand you have to throw another hat before the cooldown is done.

I think the culprit is line 44 in MysteriousCapItem.java, it's only and always getting the item in the main hand instead of checking first if the item is in the offhand or main hand.
https://github.com/Ignoramuses/bing-bing-wahoo/blob/1.18/src/main/java/net/ignoramuses/bingBingWahoo/cap/MysteriousCapItem.java#L44

Another video of this happening