surface datum disappearing

I am working on a sldrw file that is fairly complex

I am trying to place few simple surface datum symbols in several locations. 

My problem is that the symbol stays on for a little while and then mysteriously disappears.

I am running SW 2019 SP3 and I've never had this problem before. 

Does anybody know what might be going on. 

SolidworksDrawings And Detailing