This issue has been ongoing for a while now. This is across 2 realms over several characters.
Go to the bank, open bags. Right click on items to go into the bank. If they are reagents like herbs or ores they should go in to either the non-full stacks of the same in the Reagent Bank or into open Reagent Bank slots.
They don't.
I have deactivated the Bagnon add-on, used the bank in game without problem. I reactivate Bagnon and the problem comes back. And it is a random problem. One or two characters will not have it one day, then the next day the problem will reappear for them.