Upgrade to version 2004 (may 2020) giving issues with credentials

Waaromikniet You have my sympathies. This is a serious problem. I use 4 machines on a regular basis. 2 of them are oldish machines - possibly 10 years or more and 2 are much newer (1 only a few weeks old). All are running Windows 10 Pro or Home at the 2004 level. On 2 of the machines (one old and one newish) I have "this problem" - I use brackets because it's a bit difficult to say it is exactly the same problem as described here and elsewhere. On the other two machines - 1 ten years old Windows 10 Home 2004 and upgraded from Windows 7, 1 about 2 weeks old and with a brand new Windows 10 Pro 2004 system have no problems - each machine (all 4) runs with a local user id, but each machine also runs using multiple Microsoft accounts for Outlook/Hotmail email, Office 365 etc.

Let me describe the problem on 1 of the systems - this is my main machine a Dell 3620 (4 - 5 years old?) with 16GB memory. This machine uses Office (Microsoft) 365. The problem seems to focus around the Office 365 application. The Outlook client has 6 email addresses defined - 2 Hotmail, 1 Outlook, 1 BTMail (IMAP), 1 private (IMAP) account, 1 Gmail (IMAP). Outlook will be sitting there minding its own business. Sometimes it will come up asking me to enter the credentials (passwords) for 5 of the accounts - it virtually never asks me for the password for the main hotmail account. This happens once or twice per hour. Sometimes I can be working on Excel (or Word) and I come to shutdown the app and I find it wont close. I can click on the Outlook icon in the taskbar but nothing happens - I see the mini window but cannot get the window to enlarge. I go into task manager and I see nothing wrong (no unresponsive messages etc) with Outlook or Excel/Word or indeed anything else, but they just sit there. Eventually I get fed up and so I cancel Outlook from task manager, and lo and behold the whole world wakes up again. Immediately (i.e. no restart) I can start Outlook again and it will ask me for 4 or 5 passwords - sometimes in direct succession and sometimes spread over a few minutes - and everything works until the next time it forgets the passwords (in 30 mins or so). The system also seems to be unable to remember any userids or passwords for any web sites, no matter what browser I use (including Edge and Chrome). I have tried various suggestions from various user groups but none have achieved anything. I have two machines without the problem (one brand new and one ten years old) and 2 with the problem (one 4 -5 years old and one 10 years old). I did read somewhere that Microsoft seem to accept there is a problem in this area in some slightly esoteric circumstances but nothing to suggest they are in any hurry to address it.