[Baertram]

Why do you need to logout to change the addons? Isn't it working at all if you do it ingame in the addon manager?

Are you using an account name with special characters? ^°'~ etc.?

Maybe try this:
Ingame create a screenshot.
Disable all addons.
Check what folder is shown it is saved to at the top right edge of your screen and note it down.

Logout.
At char selection screne change the addons for all characters at least at 1 item and then exit the client.

Search at your file explorer in windows for the file AddOnSettings.txt
On ALL harddrive!
If you find multiple files check the last change date and time to see which one the game says is the one it uses.

It should be in c:\users\..\documents\Elder Scrolls Online\live (or your documents folder if you moved it).
If not (sometimes it was within c:\ProgramData instead).

At least it should be the same folder as the screenshot was saved to.

Check if the changes you did before logout to the addons of all chars is inside the file (edit it with a text editor and search for the addon name you have chnaged. 0 means disabled, 1 enabled. And there is a headline with the #servername-character name or #Default for all chars.

If nothing helps try to delete the file AddOnSettings.txt and recreate it.

Try to add this folder to your antivirus exclusion list then if not already done.