Firstly, I’d make sure that you have the most up to date version of the Universal AR SDK for Unity package. Are you using any other plugins, combined with the Universal AR SDK package?
I’ve not seen this error personally before, but from what I can tell, it seems to be that the OpenGL state has changed in a way that Unity was not expecting. I’d double check your player settings to make sure!
You can get to your player settings by going to File > Build Settings. Then find the ‘Player Settings…’ button. When this window opens, make sure you are viewing the ‘Player’ section. Find ‘Resolution and Presentation’ and look for ‘WebGL template’. Select ‘Zappar’. Hopefully that helps!
Have a lovely day,