Steps to reproduce the behavior:

Simply logging in produces the error

• Addon Version: 2.11 RETAIL
• ElvUI Version 12.13
• WoW Build 9.0.2 (36710)

Not sure if this is a bugsack error or WindTools:

9x ElvUI_WindTools\Modules\Skins\Core.lua:101: attempt to index field 'skins' (a nil value)
[string "@ElvUI_WindTools\Modules\Skins\Core.lua"]:101: in function CreateBackdropShadow' [string "@ElvUI_WindTools\Modules\Skins\Addons\BugSack-v9.0.1.lua"]:18: in function <...Ons\ElvUI_WindTools\Modules\Skins\Addons\BugSack.lua:8> [string "=(tail call)"]: ? [string "=[C]"]: in function OpenSack'
[string "@BugSack\core.lua"]:59: in function <BugSack\core.lua:46>
[string "=[C]"]: ?
[string "@AdiBags\libs\CallbackHandler-1.0\CallbackHandler-1.0-7.lua"]:29: in function <...ags\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:25>
[string "@AdiBags\libs\CallbackHandler-1.0\CallbackHandler-1.0-7.lua"]:64: in function Fire' [string "@!BugGrabber\BugGrabber.lua"]:147: in function <!BugGrabber\BugGrabber.lua:145> [string "@!BugGrabber\BugGrabber.lua"]:380: in function <!BugGrabber\BugGrabber.lua:294> [string "=[C]"]: in function ?'
[string "@xroll\XRoll-5.0.1.lua"]:3124: in function <XRoll\XRoll.lua:3123>

Locals:
self =

{
Blizzard_Channels = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Channels.lua:6
WeakAuras_ShowOptions = defined @ElvUI_WindTools\Modules\Skins\Addons\WeakAurasOptions.lua:177
ElvUI_AFK = defined @ElvUI_WindTools\Modules\Skins\ElvUI\AFK.lua:7
modules = {
}
CancelTimer = defined @details\Libs\AceTimer-3.0\AceTimer-3.0.lua:147
GuildInviteFrame = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Guild.lua:6
ElvUI_UnitFrames_Configure_Threat = defined @ElvUI_WindTools\Modules\Skins\ElvUI\UnitFrames.lua:11
SkinCriteriaAlert = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Alerts.lua:62
RaidUtility_ShowButton_OnClick = defined @ElvUI_WindTools\Modules\Skins\ElvUI\RaidUtility.lua:9
Blizzard_LossOfControlFrame_SetUpDisplay = defined @ElvUI_WindTools\Modules\Skins\Blizzard\LossOfControl.lua:6
Rematch_Standalone = defined @ElvUI_WindTools\Modules\Skins\Addons\Rematch.lua:796
ScheduleTimer = defined @details\Libs\AceTimer-3.0\AceTimer-3.0.lua:94
SkinItemButton = defined @ElvUI_WindTools\Modules\Skins\Blizzard\ObjectiveTracker.lua:20
ADDON_LOADED = defined @ElvUI_WindTools\Modules\Skins\Core.lua:279
ElvUI_CastBars = defined @ElvUI_WindTools\Modules\Skins\ElvUI\CastBars.lua:14
Rematch = defined @ElvUI_WindTools\Modules\Skins\Addons\Rematch.lua:904
ElvUI_SkinOptionsUI = defined @ElvUI_WindTools\Modules\Skins\ElvUI\Option.lua:7
SetEnabledState = defined @AdiBags\libs\AceAddon-3.0\AceAddon-3.0.lua:424
Hook = defined @AdiBags\libs\AceHook-3.0\AceHook-3.0.lua:274
enteredLoad = {
}
DressUpFrame = defined @ElvUI_WindTools\Modules\Skins\Blizzard\DressingRoom.lua:6
BigWigs_Plugins = defined @ElvUI_WindTools\Modules\Skins\Addons\BigWigs.lua:22
AAP_SkinOrderList = defined @ElvUI_WindTools\Modules\Skins\Addons\AzerothAutoPilot.lua:11
UnregisterAllEvents = defined @AdiBags\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:174
SkinWorldQuestCompleteAlert = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Alerts.lua:171
WeakAuras = defined @ElvUI_WindTools\Modules\Skins\Addons\WeakAuras.lua:161
Blizzard_Calendar = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Calendar.lua:6
ElvUI_ClassBars = defined @ElvUI_WindTools\Modules\Skins\ElvUI\ClassBars.lua:12
ElvUI_SkinDataBar = defined @ElvUI_WindTools\Modules\Skins\ElvUI\DataBars.lua:8
SkinLegendaryItemAlert = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Alerts.lua:236
Blizzard_DebugTools = defined @ElvUI_WindTools\Modules\Skins\Blizzard\DebugTools.lua:7
name = "ElvUI_WindTools_Skins"
StaticPopup = defined @ElvUI_WindTools\Modules\Skins\Blizzard\StaticPopup.lua:6
SkinFindGroupButton = defined @ElvUI_WindTools\Modules\Skins\Blizzard\ObjectiveTracker.lua:32
TTGameTooltip_SetDefaultAnchor = defined @ElvUI_WindTools\Modules\Skins\Blizzard\Tooltips.lua:14
Unhook = defined @AdiBags\libs\AceHook-3.0\AceHook-3.0.lua:418
WeakAuras_RegisterRegionOptions = defined @ElvUI_WindTools\Modules\Skins\Addons\WeakAurasOptions.lua:32
Blizzard_BlackMarketUI = defined @ElvUI_WindTools\Modules\Skins\Blizzard\BlackMarket.lua:6
Blizzard_IslandsQueueUI = defined @AddOns