20x Leatrix_Plus/Leatrix_Plus.lua:9281: attempt to index field '?' (a nil value)
[string "@Leatrix_Plus/Leatrix_Plus.lua"]:9281: in function <Leatrix_Plus/Leatrix_Plus.lua:9059>
[string "=(tail call)"]: ?
[string "=[C]"]: in function securecallfunction' [string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:60: in function <SharedXML/Tooltip/TooltipDataHandler.lua:55> [string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:80: in function <SharedXML/Tooltip/TooltipDataHandler.lua:76> [string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:116: in function <SharedXML/Tooltip/TooltipDataHandler.lua:106> [string "=[C]"]: in function SetAttribute'
[string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:141: in function <SharedXML/Tooltip/TooltipDataHandler.lua:134>
[string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:282: in function <SharedXML/Tooltip/TooltipDataHandler.lua:240>
[string "=[C]"]: in function securecallfunction' [string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:237: in function <SharedXML/Tooltip/TooltipDataHandler.lua:236> [string "=(tail call)"]: ? [string "@InstanceAchievementTracker/GUI.lua"]:2499: in function GetNameFromNpcIDCache'
[string "@InstanceAchievementTracker/AchievementTrackerCore.lua"]:115: in function <...nstanceAchievementTracker/AchievementTrackerCore.lua:113>

Locals:
(*temporary) = nil
(*temporary) = nil
(*temporary) = "3"
(*temporary) = "|cff33937f"
(*temporary) = "Evoker"
(*temporary) = 147.000006
(*temporary) = 127.000008
(*temporary) = "33937f"
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to index field '?' (a nil value)"
LT =

{
GuildRank = "1st Officer"
LevelLocale = "Level"
NameColor = "|cff33937f"
UnitLevel = 61
Unit = "mouseover"
GuildLine = 2
ClassCol = {
}
InfoLine = 3
RealLevel = 61
TipIsPlayer = true
NameText = "Detalzin"
PlayerControl = true
InfoText = "Level 61 Dracthyr |cff33937fEvoker"
LpTipClassColor = "|cff33937f"
Class = "Evoker"
Sex = 2
Reaction = 5
PlayerRace = "Dracthyr"
ColorBlind = "0"
GuildName = "Äsgard"
UnitClass = "EVOKER"
TipUnitName = "Detalzin"
}
LeaPlusLC = {
LeaPlusNav9 = Button {
}
WidgetTopR = "TOP"
MuteCustomList = ""
TimerY = -96
TooltipAnchorMenuTable = {
}
LeaPlusNav2.s = Texture {
}
RecentChatSize = 170
MakeFT = defined @Leatrix_Plus/Leatrix_Plus.lua:355
BordersAlpha = 0
MinimapR = "TOPRIGHT"
TipCursorX = 0
Page0 = Frame {
}
DressupItemButtons = "Off"
InviteFromWhisper = "On"
DurabilityScale = 1
MuteZeppelins = "Off"
TransHallowed = "Off"
MakeCB = defined @Leatrix_Plus/Leatrix_Plus.lua:11782
MuteGyrocopters = "Off"
ManageDurability = "Off"
AcceptPartyFriends = "On"
LockOption = defined @Leatrix_Plus/Leatrix_Plus.lua:551
RestoreChatMessages = "Off"
MinimapModder = "Off"
MakeSL = defined @Leatrix_Plus/Leatrix_Plus.lua:11728
Page4 = Frame {
}
ShowDropTip = defined @Leatrix_Plus/Leatrix_Plus.lua:280
ReloadCheck = defined @Leatrix_Plus/Leatrix_Plus.lua:608
NoPartyInvites = "Off"
NumberOfPages = 9
TipHideShiftOverride = "On"
HideZoneText = "Off"
TimerX = -5
WidgetTopA = "TOP"
SetTipScale = defined @Leatrix_Plus/Leatrix_Plus.lua:8755
SetDim = defined @Leatrix_Plus/Leatrix_Plus.lua:570
HideMiniAddonButtons = "On"
LeaPlusQuestFontSize = 18
TipShowTarget = "Off"
AutoSellNoKeeperTahult = "On"
ShowErrorsFlag = 1
NoDuelRequests = "Off"
Print = defined @Leatrix_Plus/Leatrix_Plus.lua:89
QuestFontChange = "Off"
NoRaidRestrictions = "Off"
MuteAirships = "Off"
AutoQuestKeyMenuTable = {
}
MuteSoulEaters = "Off"
HideCleanupBtns = "Off"
BordersTop = 0
Page9 = Frame {
}
ZygorToggle = defined @Leatrix_Plus/Leatrix_Plus.lua:367
TipNoHealthBar = "Off"
TooltipAnchorMenu = 1
ShowRaidToggle = "Off"
MinimapNoScale = "Off"
ShowVoiceButtons = "Off"
IsPlusShowing = defined @Leatrix_Plus/Leatrix_Plus.lua:463
MuteCustomSounds = "Off"
BlockDrunkenSpam = "Off"
LeaPlusNav5.s = Texture {
}
AutoReleaseNoAshran = "Off"
MuteMechsuits = "Off"
MakePage = defined @Leatrix_Plus/Leatrix_Plus.lua:14294
ShowWowheadLinks = "Off"
AutoQuestCompleted = "On"
Page7 = Frame {
}
CfgBtn = defined @Leatrix_Plus/Leatrix_Plus.lua:318
LeaPlusMailFontSize = 22
NoFriendRequests = "Off"
LeaPlusNav1 = Button {
}
AutoReleaseNoTolBarad = "Off"
transTable = {
}
MuteMechSteps = "Off"
WidgetTopScale = 1
NoCombatLogTab = "On"
muteTable = {
}
LeaPlusNav2 = Button {
}
MoveChatEditBoxToTop = "Off"
MuteSniffing = "Off"
MinimapY = -2
MakeWD = defined @Leatrix_Plus/Leatrix_Plus.lua:11719
LeaPlusNav4 = Button {
}
NoScreenGlow = "Off"
VehicleY = -192
Page1 = Frame {
}
LeaPlusChatFontSize = 20
LeaPlusNav0 = Button {
}
MailFontChange = "Off"
LeaPlusNav3 = Button {
}
ShowBorders = "Off"
MainPanelA = "CENTER"
BordersLeft = 0
MuteSunflower = "Off"
AutoSellJunk = "On"
AutoRepairGear = "On"
ManageTimer = "Off"
CreateDropDown = defined @Leatrix_Plus/Leatrix_Plus.lua:11946
HideTalkingFrame = "Off"
AutomateGo

This is to do with 'Enhance tooltip' ('Interface') and possibly related to Instance Achievement Tracker. You saw this error when mousing over a player unit.

• How often do you see this error?
• Starting from a /reload, are you able to list some steps that will produce this error?