SSL/TSL and port 993 are set as Google says to do.

I've had password problems in Thunderbird on both a Yahoo account and on my gmail accounts in the last five days (July 15-20 approx, 2017). I know that others had this problem 2 months ago, where the window pops up with "Google, Sign In, NEXT" etc where none of the links in the window work. Somehow the Yahoo and all the gmails but one have fixed themselves as of two days ago. On the one remaining problematic gmail address, I removed it from Tb and then had a difficult time getting it to let me add it back in; but now it's in there but won't accept my password. That same window with the nonworking links is popping up. I've gone through several suggested fix-it steps both on google (their answer 78754) and on other questions on here from two months ago that you answered to get to where I am now. Here's what I've found: It's not the version; I have 52.2.1 (32-bit) It's not the IMAP setting on the google mail account on the Google mail settings page - it's set to IMAP, and the SSL/TSL and port 993 are set as Google says to do. It's not the wrong password or a typo in the email address It's not setting Google's "allow less secure app" to Yes I've rebooted several times after making the changes that got me to where I am now, so I don't think that's the issue. One other gmail account in Tbird is set to OAuth2 but it works just fine. Another gmail acct is POP and is set to Normal Password, and it works fine (I'm told the POP mail isn't as secure). Are there other steps I can take to fix this on my own or does this continue to be an unresolved problem right now? Thank you for all you do!