I don't know if it's caused by a separate addon, but opening the map currently gives me 4 errors in Mapster:QuestPOI_OnAcquired when it goes to call pin.NormalTexture saying that it's a nil value. Additionally, I would get a new error every time I moused over a world quest on the map. All errors stopped occurring when I commented out that line.

I was not able to reproduce this without any map addons so far.

I think it was HandyNotes. Not 100% sure though because several addons were causing errors with the map and WQs, but after updating/fixing some of them, this stopped happening.