Login error via Cloudflare with Nginx Proxy Manager

I have a problem logging in through my URL https://homeassistant.randomdomain.eu/
If I log in locally by IP address everything works.
After entering username and password comes the two factor authentication. Until then everything works. When I then confirm I only get to “Start over” again.
Then I can start all over again with the same problem.
Through these login attempts I get the following log messages:

I am using HA on my Unraid server as a VM. The Unraid server is also running the Nginx Proxy Manager.
In my Cloudflare account a CNAME DNS record is set for “homeassistant” which points to an A DNS record which then forwards to my public IP.
In the Nginx Proxy Manager a Cloudflare SSL certificate is set up for full encryption.

If any configs or logs are needed I can post them of course.

Did you find a solution for this?