Can't login anymore

tried to login into cockpit cms. and i just come back to the login screen.
looked into the files, googled (found stuff, tried it, did not help).
backuped my data and reinstalled a fresh cockpit cms, called /install, tried the standard user. back to login screen.

tried a different computer, different browsers, nada.

started a local server, tried the /install and standard user thing. everything works like a charm…

last week everything worked and today nada. maybe one of you can help?