currently the issue with banks in general is they load every time you change zones, they also take up a majority of the rendering when they are close and not even near the bank, let alone opening them all up to view.
since this expansion now even having any tabbed slots will cause some bags to be missing depending on how many bank slots the player has. only fix for this is to reduce the amount of bags that are open or have a secondary inventory tab just for bags to show them all when tabbed over.
i thought this problem was suppose to be fixed when 64 came around to increase use for Ram but ehh apparently its "working as intended" or so im told. as of yet i dont see a work around or a way to increase memory to have tabbed bank and 12 inventory slots all open at once.