NAS540 login failed after upgrade to V5.21 (AATB.4)

Hello.

Recently, I am struggling to properly access my NAS540 Web interface.
I have realized, that after the reset/power cycle of the NAS, the web server is not started. As I have ssh already enabled, I was able to start it manually and proceed the operations of my NAS.

After I login successful (after few days if troubleshooting, I was notified, that new FW is available (V5.21 (AATB.4)). So I have updated my NAS immediately hoping, that the issue with the WebServer will be resolved by the update.

Unfortunately, the situation got even worst. The Web Server still do not start automatically and I had to start it manually (it is not the best solution, but manageable, until the final solution will be available).

But moreover, now after the upgrade and start of the Web server, I can get to the login page, but the credentials are not accepted. I can ssh the NAS with those credentials, but not able to login.

Could you please help me to understand, what might went wrong?

Thank you
Miro