Apparently, this a recent, common issue with LeEco phones. I found two threads:
https://www.reddit.com/r/Smartphones/comments/o24j6t/2_weeks_ago_my_smartphone_keeps_trying_to_sign/
https://androidforums.com/threads/insistent-sign-in-to-network-pop-up.1336192/
The first one talks about a easy...