33x ...faceDragonflightUI/Mixin/ItemColor.mixin.lua:359: attempt to index global 'GuildBankFrame' (a nil value)
[string "@DragonflightUI/Mixin/ItemColor.mixin.lua"]:359: in function `UpdateGuildBankSlots'
[string "@DragonflightUI/Modules/UI.lua"]:102: in function <DragonflightUI/Modules/UI.lua:77>

Locals:
self =

{
AddOverlayToFrame = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:14
HookInspectFrame = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:112
HookCharacterFrame = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:81
UpdateGuildBankSlots = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:351
OnEvent = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:8
HookGuildbankBags = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:336
UpdateAllBags = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:217
HookBags = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:143
UpdateMerchantBuyback = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:317
UpdateBag = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:234
UpdateMerchant = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:275
UpdateOverlayQuality = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:57
UpdateBankSlots = defined @DragonflightUI/Mixin/ItemColor.mixin.lua:257
}
activeTab = 1
itemButton = nil
buttonID = nil
texture = nil
itemCount = nil
locked = nil
isFiltered = nil
quality = nil
(for index) = 1
(for limit) = 7
(for step) = 1
c = 1
(*temporary) = nil
(*temporary) = "Column1"
(*temporary) = "1"
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to index global 'GuildBankFrame' (a nil value)"

Hm, the error doesn't really make sense, so it might be something else. Or its some obscure blizzard bug.
Anyway, I added a simple guard to check if the GuildBankFrame exists: 4ec86f6

Maybe you could test it out if you can reproduce the error, its a simple 1 line change.