I'm not sure if my issue is a duplicate of this bug or not. My issue is New mail is not checked on startup when Check On Startup (selected for both Pop accounts) is selected for combined Inbox for 2 POP accounts. Usually I see mail on my phone first ( does not change data on POP servers ). My Get Mail button works fine and after doing initial Get Messages selection the timed mail checks seem to be working OK. POP1 is set as default account.

Looking in my config file, the combined (POP1name,POP2Name) is set as the default to download first. I tried changing setting to POP1 in config to be the first downloaded, no change - still fails. Interestingly I have a little used Gmail IMAP account, if I just set that to the default account, send an email from it to one of my POPs, close Tbird, then reopen, it will get new email on startup. I looked at 267062 - I am seeing status check at the bottom.

Also the problem seems to be with the first time I open Tbird for the day in some way. I noticed that if I close Tbird after doing the Get Messages, which is normal behavior open / close several times a day, when I go in / out and then reopen Tbird the new messages on startup downloads.

History is 68.5 since Feb 26, 68.4.2 on Jan 30, and 68.3 on Dec 5th. When did this start ? somewhere in there. I am so automatic in hitting the Get Messages button, e.g. read the newspaper link daily, that since the new mail downloads after the first hit, just not paying attention. Usually triggered to look by my phone. Plus, I am on Spectrum broadband with a roadrunner POP ( former TWC account ). That is my default account. They changed the TWC webmail over to the "new" Spectrum webmail last summer ?? Since then I have to log on to Spectrum webmail everyday to check for them marking good messages as Spam and add filters to Rarely did this with TWC. Example my test messages labelled Test send from my roadrunner to roadrunner went to Spam. I think the general suspicion on Spectrum has masked me from noticing the change in new mail behavior.

Update, after leaving Tbird up most of the day after just hitting the Get Messages button once in the morning, new messages came in fine. So, this evening, I closed it and re-opened it and the new messages on startup worked as normal. So I did not change anything specific with Tbird settings or accounts during this time, but this morning Windows 10 applied KB4540673 which is a Security update with no real data about what they changed. So right now my Tbird is working normally with 68.5 with 2 POP accounts glomed together for a shared Inbox.

Sorry for raising a flag. ( Last night I did reinstall 68.5 from scratch and restored my Profile and Data from a Macrium Reflect File and Folder backup.)