Resolved Problem logging into a MS account

Background:
I have three Windows 10 devices at home - one in the study, my Surface Pro, and a PC in the lounge to show things on the TV. These three share a common account that is linked with an MS email address. This means I can log in on one and if either of the others are powered up I can seamlessly connect thru the network to either of the "Public" or that user's files (i.e. C:\Users\<user> files). i.e. no password prompt.
Some of my userids are local accounts, and they also seemlessly connect (deliberately set up with the same password of course).
The PC used on the TV also acts as a file backup for the one in the study; I have a sync-ing product set up to ensure all files in Public are copied across, along with some other file shares. I get no password prompt from doing this. This forms one of my "file backups" methods. Of recent though, this 10yr old PC is struggling to function properly - it can take up to half an hour to get completely logged on(!) and now frequently needs a reboot instead of waking from 'sleep' state.

The problem:
Time for an upgrade I said "well done good and faithful servant"! So I purchased a replacement PC and set it up the same. But I have a problem I have been unable to solve.
If I log on to any non Microsoft local-only account (std or Admin), they connect seemlessly to the other devices without any "give me a password" prompt and show me the file structure I expect to see.
BUT ... if I log onto the MS email linked address account, it reports incorrect password (no it ain't!) and requests I provide it with the correct one. The file structure is exactly the same too - "C:\Users\<user>" and obviously "C:\Users\Public".
Now I know the password is correct, because the user setup has been pulled thru by the MS account and the Office 365 installation was successful.
I have deleted and re-setup the userid (twice) in case of something odd happening, but nothings changed. problem still exists.
I can provide it an alternative password using one of the local (std) accounts - that works. But I need the 'same' MS account userid to authenticate so i see the files it *should* have access to.

Anyone have any ideas what is wrong and how I can fix it? Seems strange it's working on 3 machines but not the 4th.

Thanks.

 

Are we to assume that the new PC is running W10 or is W11?
All comps running the same version ie. Home or Pro with all MS updates installed?

 

All PCs are running Windows 10 Home fully patched up to date, except Surface Pro which is Win 10 Pro (fully patched).

The new PC technically reports Win 10 Core which I believe is another name for 'Home' (why MS changed the name, no idea!).

 

In W10 > Start > Settings > Accounts > Sync your settings > all OK or attention required?

You may need to Verify your "new" comp.

 

All looks ok there, no errors reported. Sync settings is ON, all individual sync settings are also ON.

The loaded theme, desktop background, etc all got downloaded and match with the other machines.

 

Well, having a holiday from the computer seemed to give the new computer time to think about it's problem, not that I left it powered on.
Booting it up after getting back, and loading the latest MS update 21H2 on, it now works as expected. Can't see the update was the "fix", I guess it was a case of "give me time mate!".

Still at a loss as to why it failed at all of course but now I've never really know why.

 

Thanks for the update. Nice Xmas present.