Could be a problem of pyOpenSSL.
"…TypeError: must be X509, not ComparableX509"
I removed pyOpenSSL
sudo pip3 uninstall pyOpenSSL
and then tried to reinstall it. But this failed, the box still found an old version.
So I repeated the uninstall command to remove the older version, too.
Then I was able to reinstall pyOpenSSL
sudo pip3 install pyOpenSSL
I hope, this fixed the box. Tommorrow (after a second time of 7 days of suffering) it will be allowed to get new certificates from letsencrypt.