Bugtracker/buggrabber discovered it

`6x AllTheThings/AllTheThings.lua:22625: Attempt to access forbidden object from code tainted by an AddOn
[string "=[C]"]: in function `GetOwner'`
`[string "@AllTheThings/AllTheThings.lua"]:22625: in function <AllTheThings/AllTheThings.lua:22620>
[string "=(tail call)"]: ?`
`[string "=[C]"]: in function `securecallfunction'd`

[string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:60: in function <SharedXML/Tooltip/TooltipDataHandler.lua:55>
[string "@SharedXML/Tooltip/TooltipDataHandler.lua"]:77: 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 "@Blizzard_NamePlates/Blizzard_NamePlates.lua"]:860: in function <...eBlizzard_NamePlates/Blizzard_NamePlates.lua:853>

Locals:
Skipped (In Encounter)`

This is one of those issues where it might not be specifically ATT's fault. What seems to be the case as far as is revealed by the error information, is that ATT was trying to check information of a tooltip while you were in combat within the M+ instance. But some part of the information of that tooltip was touched by an addon and not allowed to be retrieved while both in an instance and in combat. Would be curious to know if this still occurs for you if you disable the In Combat option under ATT > Tooltips settings.

Also did this happen just ONE time or is it a typical occurrence in M+ runs? Seems very strange for this situation to only have happened once if all it takes is rendering a tooltip during combat in M+. I personally have never had this happen with ATT enabled in combat within M+ dungeons, so it makes me think that another addon is contaminating the nameplates/tooltips while in combat in M+.

It seems to happen randomly. Sometimes I get the issue, sometimes I don't.

I don't have any nameplate addons but I have the M+ timer WA from Reloe, I wonder if that could cause it? Buggrabber isn't showing me any other issues that specifically pop up in M+ (Fishing Buddy is showing me 2 minor bugs on every manual /reload or when I log in - but that addon is currently being re-built from the ground up).

I'll disable In Combat for now and see what happens.

I forgot to disable in combat but it happened exactly 2 times in Shadowmoon Burial Grounds (+8 if it matters). First time it happened right after the second boss, when clearing the trash.

Second time it happened right after the third boss, when my group let the spiders cast the DoT and I manually targeted the healer to dispell them.

Same issue as before, but like I said, I forgot to disable In Combat :(