Just mousing over certain items causes an error that continues to fire so long as you hover over the item. The Nightcloaked Helm is one, for me. Blackhound Headguard is another.

15x BetterWardrobe\Modules\BlizzardAPI.lua:179: attempt to index global 'BetterWardrobeCollectionFrame' (a nil value) [string "@BetterWardrobe\Modules\BlizzardAPI.lua"]:179: in function <BetterWardrobe\Modules\BlizzardAPI.lua:175> [string "=(tail call)"]: ? [string "@BetterWardrobe\Modules\Wardrobe-Appearances.lua"]:4628: in function GetSetSourceData'
[string "@BetterWardrobe\Modules\Wardrobe-Appearances.lua"]:4648: in function GetSetSourceCounts' [string "@BetterWardrobe\Modules\Tooltips.lua"]:395: in function ShowTooltip'
[string "@BetterWardrobe\Modules\Tooltips.lua"]:75: in function <BetterWardrobe\Modules\Tooltips.lua:73>
[string "=[C]"]: ?
[string "=[C]"]: ?
[string "=[C]"]: ?
[string "=[C]"]: in function SetBagItem' [string "@FrameXML\ContainerFrame.lua"]:1371: in function ContainerFrameItemButton_OnUpdate'
[string "@FrameXML\ContainerFrame.lua"]:1418: in function `ContainerFrameItemButton_OnEnter'
[string ":OnEnter"]:1: in function <[string ":OnEnter"]:1>

Locals:
setID = 50018
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to index global 'BetterWardrobeCollectionFrame' (a nil value)"
addon =

{
ViewDelay = 3
useAltSet = false
modules = {
}
Sort = {
}
SecureHook = defined @BetterWardrobe\Libs\AceHook-3.0\AceHook-3.0.lua:336
tooltip = BW_ProfileTooltip {
}
SetDefaultModulePrototype = defined @AckisRecipeList\libs\AceAddon-3.0\AceAddon-3.0.lua:409
MogIt = {
}
IsEnabled = defined @AckisRecipeList\libs\AceAddon-3.0\AceAddon-3.0.lua:451
GetActiveCategory = defined @BetterWardrobe\Modules\CollectionList.lua:217
RefreshCharConfig = defined @BetterWardrobe\Modules\Core.lua:997
RegisterMessage = defined @tomtom\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:90
UnregisterMessage = defined @tomtom\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:153
validSetCache = {
}
ArmorSetModCache = {
}
db = {
}
SetEnabledState = defined @AckisRecipeList\libs\AceAddon-3.0\AceAddon-3.0.lua:424
Hook = defined @BetterWardrobe\Libs\AceHook-3.0\AceHook-3.0.lua:274
GetSourceFromItem = defined @BetterWardrobe\Modules\Tooltips.lua:208
InitExtendedSetsSwap = defined @BetterWardrobe\Plugins\ExtendedTransmog.lua:6
OnEnable = defined @BetterWardrobe\Modules\Core.lua:1207
RefreshOutfitData = defined @BetterWardrobe\Modules\Core.lua:874
GetArtifactSourceInfo = defined @BetterWardrobe\Modules\ArtifactAppearances.lua:283
IsWeaponCat = defined @BetterWardrobe\Modules\CollectionList.lua:222
ItemAppearance = {
}
OnInitialize = defined @BetterWardrobe\Modules\Core.lua:1017
NewModule = defined @AckisRecipeList\libs\AceAddon-3.0\AceAddon-3.0.lua:235
Globals = {
}
SortSet = defined @BetterWardrobe\Modules\SortingFunctions.lua:509
HiddenAppearanceDB = {
}
GetName = defined @AckisRecipeList\libs\AceAddon-3.0\AceAddon-3.0.lua:279
C_TransmogCollection = {
}
Camera = {
}
name = "BetterWardrobe"
UI = {
}
Disable = defined @AckisRecipeList\libs\AceAddon-3.0\AceAddon-3.0.lua:314
GetSetType = defined @BetterWardrobe\Data\DataBase.lua:656
Unhook = defined @BetterWardrobe\Libs\AceHook-3.0\AceHook-3.0.lua:418
Print = defined @AckisRecipeList\libs\AceConsole-3.0\AceConsole-3.0.lua:54
IsFavoriteItem = defined @BetterWardrobe\Modules\Wardrobe.lua:3436
usableSourceCache = {
}
ExtendTransmogView = defined @BetterWardrobe\Modules\TransmogVendor.lua:423
BuildClassArtifactAppearanceList = defined @BetterWardrobe\Modules\ArtifactAppearances.lua:177
TRANSMOG_SET_FILTER = {
}
Init = {
}
CreateChatLinkTransmogVendor = defined @BetterWardrobe\Modules\ImportExport.lua:299
EventHandler = defined @BetterWardrobe\Modules\Core.lua:1314
SelecteSavedList = false
CollectionList = {
}
GetSetCounts = defined @BetterWardrobe\Modules\BlizzardAPI.lua:487
RemoveItemSubstitute = defined @BetterWardrobe\Data\DataBase.lua:866
UnregisterEvent = <`