As some of you may have noticed, we were constantly struggling with the SSL certificates, because the previous procedure did not work anymore. After a long night or rather very long early morning, we finally found a solution. The Certbot brought inexplicable error messages, which nobody could understand. LetsEncrypt made some changes to the bot that led to these errors. After almost two days of searching we finally found a solution. The certificates are now up to date. Many thanks also to Andrea for the hints with the errors.
Should anyone find any more bugs, please let us know. Thank you.