It looks like a bug - I've managed to reproduce it myself thanks to the details you provided. I filed a bug report (case 737565). It seems to be having problems with static constructor of "Publisher" type. As far as I can tell, the static constructor is using reflection to get a specific method with specified parameters. IL2CPP is trying to find it and fails when retrieving the default value of a parameter because the parameter type is not initialized and we think it should be. To workaround for now, you can delete that assert... it doesn't seem to be crucial.