I tried /reloadui and relogging as that sometimes helps, but in this case it didn't. When I moved to a new area, the icon even disappeared from my map. At least I don't see it anymore so I won't run back to it all te time thinking I missed a ruin
I reported it ingame as a cosmetic bug. It won't cause sleepless nights, but it should be fixed anyway/
As a completionist this is infuriating. I can't in good conscience move on to the next area without this being fixed. It seems minor (and it really is) but it needs to be fixed. And I assume it would not be hard to do?