EX2 Ultra - Credential problem after update to firmware 5.19.117 - solved

So I got a new WD Mycloud EX2 Ultra 8Gb a few days ago.
Created Shares, users and migrated all our data from an old Netgear RN102. This all went fine.
The shares are private and have a couple of users with explicit credentials(read only, read/write or none).
All worked well from a mutli-user windows 11 machine and android devices.

So then the WD Ultra got a firmware update today from 5.18.117 to 5.19.117…(and one yesterday from a previous one to 5.18.117).
Except for one user (myself), all others cannot access their shares anymore. Not on Windows 10,11 or android.
The log gives many errors like:
CIFS: Authentication for user [xxxxx] has FAILED.

Changing the shares to public access remedies the situation but is far from ideal.
I have seen al sorts of solutions varying from registry changes to SMB changes etc.
Anyone with a good solution? It sounds quite ridiculous that I would have to mistrust every update.

Update january 13:

I made a discovery. If I set my shares all to public within the dashboard and then use Windows Explorer/security tab to set directory security then I have the control I want and works for all(!) devices, including android.

example: I have a Share named ‘Data’ that I give public access. I then make directories within that share. Each directory can have its security changed from Windows, so if I give a user Read & Execute, List Folder Contents, Read rights for that directory they can see and read everything but not create, delete or modify anything. I can do this with any number of users and the access rights that I want. The only drawback is that I cannot add groups from the EX2 Ultra to the security, only users.
Is this the way it should be done? If so then someone should modify WD’s documentation…

n.b. Actually, this is quite the normal way of working within Windows, create shares with everyone ‘full control’ and set security on the subsequent directories with groups(preferably) or users. My old Netgear worked pretty much the same.

Update January 14

Yesterdays update did not work well. Windows security on a directory causes strange things on other directories on the same share as well.
BUT I solved it. I migrated from my old Netgear NAS to a new EX2 Ultra using Netgear’s backup program(Nas to NAS, is fast…). The migration worked in Admin context on both sides and created directories with Admin as the creator/owner (amongst others),
The directories on the shares didn’t ‘like’ this and function only well when public.
So I created new directories with the same names using my own ‘full control’ user account and cut&pasted all data to the new directories. This took a while as all credentials had to be replaced on all subsequent files and directories. Now everything works as it should. The new firmware was NOT the culprit but just a coincidence.