I do he the Thunderbird data on a NAS accessed over a LAN. I've been doing that for a long time with no issues.

I beg to differ, you are having password issues and have been for some time. You are one of a very few reporting such an issue. If you profile is stored locally do you see this? My guess is no.

Thunderbird is built on the expectation the profile folder will be located on the local drive and accessible in extremely short time frames, not the long lead times we commonly see in Network access where bandwidth is measured in MegaBits per second instead of the local storage where it is measured in Gigabytes per second.

Now generally on a quit network without much happening Thunderbird will perform reasonably well on network share of NAS, but it is something that is version dependent and network saturation dependent. Thunderbird is not tested accessing a network share for it's profile, so essentially any access change could see a version arrive with serious access issues on the network. I have seen a number over the years.

A couple of examples are https://bugzilla.mozilla.org/show_bug.cgi?id=1537784 and https://bugzilla.mozilla.org/show_bug.cgi?id=1497819 I am sure there are many more.

I am pretty sure you are seeing some sort of race condition where Thunderbird asks for the file, but does not get it so just writes an empty one and gets on with life by asking for a password. I should point out that for accounts with the oauth authentication method there is no password stored, only the oauth token. So password manager without passwords are becoming somewhat normal anyway.

Thanks for the reply. I have the profile on the NAS for a reason...and haven't tried moving it so I can't confirm your suspicion its the NAS location. I looked at your links and saw one indicating it was adding "tmp" to some files when it can't access them. I searched the profile folder and didn't have any such files now, but next time the error arises I'll look again.

I'll add that the problem is (very) intermittent. I'll have it several times over a few days, and then weeks or months with no issue.

Also, if I start Thunderbird when not connected to the network...I just get an error that the profile cannot be found. When connected...it starts up. From loose memory, I think the issues arose more often (but not always) right after startup/login. Assuming the connection was busy with startup nonsense--that might support your busy/slow traffic theory.

I'll also add details about the oauth tokens. Normally I will see them and a lot of passwords listed in the saved password list of Thunderbird. As I noted above, the passwords will disappear, but the oauth tokens are still listed. That said...they are 'broken' too. Just as I need to re-enter passwords, a popup dialog box appears from Microsoft/Outlook that asks for more info (sometimes just the password for the account and sometimes it demands I give it the recovery email for those accounts and get a code sent there. While you didn't say it directly, I got the impression you were implying that because they are 'tokens' they aren't/shouldn't be affected. They are. I don't know if broken tokens affects the NAS theory.