After updating to WP 5.4.2 I am getting this error message when I try to access the site

HTTP redirect status code must be a redirection code, 3xx.

At first I could see some pages and access the dashboard. I could change themes and I could deactivate plugins but I could not activate or reactivate them. Also I could see the regular public pages in the browser. But now I can't access anything at all. Has anyone seen this before?