During daily use, at startup Lightroom CC prompts to sign-in multiple times per week, sometimes multiple times per day. Desktop CC running or not seems to make no difference. Once per month would be a more reasonable schedule. Menu/help/sign-out is never chosen.
Are you signing out of Adobe Creative Cloud when closing Lightroom? If so, don't. That deauthorizes your Creative Cloud apps on your computer. Just stay signed in to Creative Cloud and just exit from Lightroom to close Lightroom.