I saw this in some addon where you keep track of your toons/characters.
The name of the dev was in the addon name but cannot remember it anymore in detail.
What addons are enabled as it heppens for you? Could you provide a list, maybe I can see the name and remember it then.
It's an addon keeping track of moutn timers, active quests and soon, across your toons.
Edit:
I think it was this addon:
https://www.esoui.com/downloads/info...sAltholic.html
From the addon description:
You can use "/leoalt checklist" to show/hide the checklist
Perhaps this helps to hide it.
If not:
Maybe you need to logout and delete the SavedVariables of this addon, and build them new for your chars.
Or, if the error remains the same, tell the author in the addon comments to please investigate and fix the checklist.