Realy strange problem with Site-URLs and truncated posts

Hello there,
i am expering realy strange problems when navigating to my WP-Blog from different urls.
So the original URL ist
https://berlani.de (everything is fine here)
So I wanted to change it to something more personal
https://jakob-r.de (what happens here?)

Of course you have to change the settings to the new URL but this did not do any good.
And other URLs are working fine!
https://www2.jakob-r.de, https://test-test.berlani.de
Everything normal here! Just the standard URLs the one with and without the www won’t work.
I don’t have the slightest idea and I can not recognize any pattern in the truncation of the posts.
May be you have an idea!
I am really puzzled. ??