I've been having a lot of issues with the skins not applying. I believe it started with an ElvUI update, possibly 13.23 which is what I am currently using. However today I got an actual lua error and wanted to provide the information.

https://pastebin.com/EVb6mnV7

474x AddOnSkins/Core/API.lua:970: attempt to index local 'icon' (a nil value) [string "@AddOnSkins/Core/API.lua"]:970: in function SkinTexture'
[string "@AddOnSkins/Skins/Mainline/Blizzard/Merchant.lua"]:80: in function <...dOns/AddOnSkins/Skins/Mainline/Blizzard/Merchant.lua:79>
[string "=[C]"]: in function MerchantFrame_UpdateCurrencyButton' [string "@FrameXML/MerchantFrame.lua"]:927: in function MerchantFrame_UpdateCurrencies'
[string "@FrameXML/MerchantFrame.lua"]:33: in function showFunc' [string "@FrameXML/PlayerInteractionFrameManager.lua"]:183: in function <FrameXML/PlayerInteractionFrameManager.lua:172> [string "=[C]"]: in function ShowFrame'
[string "@FrameXML/PlayerInteractionFrameManager.lua"]:215: in function <FrameXML/PlayerInteractionFrameManager.lua:212>

Locals:
self =

{
SkinAchievement = defined @AddOnSkins/Skins/Mainline/Blizzard/Achievement.lua:11
Blizzard_Channels = defined @AddOnSkins/Skins/Mainline/Blizzard/Channels.lua:11
Blizzard_AbilityButton = defined @AddOnSkins/Skins/Mainline/Blizzard/ExtraButtons.lua:3
ArrowRotation = {
}
modules = {
}
CancelTimer = defined @ElvUI_Libraries/Core/Ace3/AceTimer-3.0/AceTimer-3.0.lua:147
FindFrameBySizeChild = defined @AddOnSkins/Core/API.lua:1075
Blizzard_ItemSocketingUI = defined @AddOnSkins/Skins/Mainline/Blizzard/Character.lua:441
GradientHighlight = defined @AddOnSkins/Core/API.lua:180
Blank = "Interface\AddOns\ElvUI\Core\Media\Textures\White8x8"
SkinIconButton = defined @AddOnSkins/Core/API.lua:600
ScheduleTimer = defined @ElvUI_Libraries/Core/Ace3/AceTimer-3.0/AceTimer-3.0.lua:94
AllTheThings = defined @AddOnSkins/SkinsAllTheThings.lua:5
ADDON_LOADED = defined @AddOnSkins/Core/Core.lua:161
SkinErrors = {
}
BuildProfile = defined @AddOnSkins/Core/Options.lua:185
data = {
}
UIScale = 0.711111
db = {
}
SkinBackdropFrame = defined @AddOnSkins/Core/API.lua:918
AdjustForTheme = defined @AddOnSkins/Core/API.lua:985
SetEnabledState = defined @ElvUI_Libraries/Core/Ace3/AceAddon-3.0/AceAddon-3.0.lua:420
Hook = defined @ElvUI_Libraries/Core/Ace3/AceHook-3.0/AceHook-3.0.lua:273
Options = {
}
Font = "Fonts\ARIALN.TTF"
events = {
}
Noop = defined @AddOnSkins/Init.lua:39
SkinTrimScrollBar = defined @AddOnSkins/Core/API.lua:749
Blizzard_Mail = defined @AddOnSkins/Skins/Mainline/Blizzard/Mail.lua:3
SkinWidgetContainer = defined @AddOnSkins/Core/API.lua:1191
Media = {
}
SkinSlideBar = defined @AddOnSkins/Core/API.lua:804
SkinTooltip = defined @AddOnSkins/Core/API.lua:949
EmbedSystem_WindowResize = defined @AddOnSkins/Embed/ElvUI.lua:82
EnumObjects = defined @AddOnSkins/Core/API.lua:1023
Blizzard_Calendar = defined @AddOnSkins/Skins/Mainline/Blizzard/Calendar.lua:12
GetChatWindowInfo = defined @AddOnSkins/Embed/Core.lua:35
CleanTexture = defined @AddOnSkins/Core/API.lua:78
EmbedEnterCombat = defined @AddOnSkins/Embed/Core.lua:168
GetName = defined @ElvUI_Libraries/Core/Ace3/AceAddon-3.0/AceAddon-3.0.lua:275
GetOptions = defined @AddOnSkins/Core/Options.lua:292
Blizzard_DebugTools = defined @AddOnSkins/Skins/Mainline/Blizzard/DebugTools.lua:3
name = "AddOnSkins"
Disable = defined @ElvUI_Libraries/Core/Ace3/AceAddon-3.0/AceAddon-3.0.lua:310
SkinLibraries = defined @AddOnSkins/SkinsLibraries.lua:154
BugSack = defined @AddOnSkins/SkinsBugSack.lua:5
Unhook = defined @ElvUI_Libraries/Core/Ace3/AceHook-3.0/AceHook-3.0.lua:417
Print = defined @AddOnSkins/Core/Core.lua:92
preload = {
}
Blizzard_IslandsPartyPoseUI = defined @AddOnSkins/Skins/Mainline/Blizzard/BfA.lua:69
SetOutside = defined @AddOnSkins/Core/API.lua:69
Init = defined @AddOnSkins/Core/Core.lua:334
Blizzard_BlackMarketUI = defined @`