Thank you all, I could resolve the issue. Problem was a somewhat faulty certificate that a
user had loaded into the userCertificate attribute of its LDAP entry.
I could see it by using cat /var/log/httpd/error_log
ValueError: unable to convert the attribute 'usercertificate' value
b'-----BEGIN CERTIFICATE-----\\nMIIEaDCCA1CgAwIBAgI .... X5xy7CQ==\\n-----END
CERTIFICATE-----\\n' to type <class
'cryptography.x509.base.Certificate'> in LDAP entry
'uid=test-user,cn=users,cn=accounts,dc=test,dc=intra'
removing the userCertificate attribute of this entry got all 3 freeIPA instances back
running and the web interface error free.
Thanks,
Nico