Hello @Kevo,
have you seen the comment at your bug report?
Apps that use the vhost feature from bug 45115 are probably incompatible with the current way the letsencrypt app handles the apache2 config.
In the apache2 config univention-letsencrypt.conf should be a line IncludeOptional /etc/apache2/ucs-sites.conf.d/*.conf
So it may be enough to link the jitsi apache2 config to that directory ln -s /var/lib/univention-appcenter/apps/jitsi/config/vhost.conf /etc/apache2/ucs-sites.conf.d/
Have you tried that and did it resolve your issue? Would be good to know. Thank you.
Best regards,
Nico