I get Not Responding too often

What is your anti-virus software?

Anti-virus is the default Windows Defender. In virus settings: Real-time protection is On, Dev Drive Protection is On, Cloud-delivered protection is On, Automatic sample submission is On, Tamper Protection is On, Controlled folder access is Off, Exclusions - the only exclusion is my Thunderbird profile folder.

I believe these are all default settings - I haven't change anything except adding T as an exclusion.

I hope that gives a clue. Thanks for your help. Alan

Exclusions - the only exclusion is my Thunderbird profile folder.

I'd have suggested that next if the exclusion were not set yet. That should eliminate anti-virus software as the culprit for the 'Not responding' issue.

Is there any other kind of security software you may run?

You can try to start Windows 10 in safe mode with networking enabled.

Does the problem go away?

This is a troubleshooting step, not a solution.

Wrt the disappearing passwords, are you running any kind of cleaning software like CCleaner?

The only antivirus is via MS Defender and I don't have CCleaner. In Windows Safe mode it was still deleting the saved passwords. I have however made progress by completely uninstalling Thunderbird and deleting all Mozilla files that remained on the C drive (an SSD). Then I moved my profile from the NAS to the C drive, reinstalled Thunderbird, pointed it at my copied profile on C. Interestingly, moving the profile took a very long time; the old profile had 2234 files in 140 folders taking 855mbytes, including hundreds of very small files which slowed it down (a lot of them may have been empty files in very many archive folders). The new profile has 771 files in 124 folders taking up 841mbytes. Now T is working pretty fast in opening. loading and deleting emails and so far it has not deleted my passwords. I have added T as an exclusion in the MS antivirus but it was fast enough before and no faster after. There still seem to be a lot of redeundant files in the profile - for example there are 17 prefs.js files; all but the first are dated in 2020 only prefs.js is dated today. There are several abook.sqlite files. There were several blocklist files taking up 1.6mbytes (dated 2017 to 2020) - out of date?; but now there is a blocklists folder dated today needing 1.1mbytes. There is a file AlanProfile dated 2011 pointng to a D: drive which I no longer have. These redundant files may not affect performance but it would be nice to get to a clean profile; but it contains all my emails (in the ImapMail and Mail folders and possibly elsewhere) so may not be easy to do. I will look further on the forum and perhaps raise a new question/topic. Many thanks for your help.