Some marker icons cannot be removed anymore as they were applied to items (bound, stolen) before a bug fix prevents this now.
So how can I remove them now?

You are able to change the "only unbound" in the settings of the marker icon "sell to guild store".
https://www.esoui.com/portal.php?id=136&a=faq&faqid=174

Research is only available if the item is a gear (armor, jewelry, weapon) and if you use a dynamic icon you can setup each icon to do this research (gear) check too, like described here:
https://www.esoui.com/portal.php?id=136&a=faq&faqid=125


If you want to remove the marker icons on those items use the SHIFT+right mouse button (needs to be enabled at the settings menu -> marks -> Undo)

or enable the "Remove/Undo context menu entry" (same settings menu) so you can remove all marker icons directly at the context menu:


or apply any other marker icon which you have setup to remove existing ones (Automatic de-marking), e.g. "Mark for normal sell", and then remove it again.