Multisite Network Admin – Access Denied

Hi all,
Today I had a very strange experience with my multisite installation. It all started that my User / PW combination was not accepted when trying to log in. I tried several times but nothing changed. I decided to reset the PW. After that I could log in. I started to do some minor changes on the main page. This worked well. After that I switched to the subdomain page to do the same changes there. I reached the subdomain dashboard and tried to open the page with Elementor. That failed. I tried in Safe Mode and followed all other hints I could find in the internet. Nothing worked. I tried a restore (UpdraftPlus). I chose the oldest backup (6 weeks old). This failed with the hint that the site which was backed up would have been an http and not an https site. (very strange because I never changed anything on this setup). I tried to restore the last backup. After the restore process I had to log in again. The new password was not accepted, so that I had again to renew it. I could login then. The restore was successful but the behaviour remained the same. Could not be opened with Elementor. I have an additional subdomain site for test reasons. I tried to open it with Elementor and found the same problem. Then I tried to access the network admin dashboard and the access was denied even though my role is super administrator.
Any ideas what could have caused this and what measures I could take?
Thank you

The page I need help with: [log in to see the link]


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