Click on the identity plate and it will then show you the option to pause the Lightroom mobile.
I have LR 6.2.1 - I cannot see any option to pause Lightroom mobile. I get always the prompt that I was signed out of mobile sync and shall login again.
I have this annoying error message always when starting LR since I upgradet to LR 6.2. This is very annoying, I am not a LR mobile user and don't want it to be.