I searched for solutions. Created new accounts. Now all three accounts have the same problem. I suspect because I use sync, it's also affected (infected?) my home computer(s). For security purposes, I don't leave my browser open all day, so I have to start every session with going to settings and switching it on. this has to be at least 10 times per day.

I don't want to convert to Chrome, but it seems nobody has an answer to this. I thought the latest update with the new password manager might fix it, but that just made everything worse. Not only doesn't the checkmark stick, but I can't see a list of sites and passwords any more. I only get an abbreviated list and can check one password at a time. This really sucks, but is another issue.