Caught in a loop when logging into trailhead.

Dear Community! 

Since a couple of weeks I experience a problem when logging into trailhead. After adding the mail sent pin I get forwarded to

which does not stop loading i.e. is caught in a cycle. 

I can remedy that by going back to the trailhead page and slam "login" again. Than I get forwarded to my "today" page as usual. 

Any ideas what causes this problem ... and how to fix it.  

Cheers