How can that be? (someone suggested that it's because my server needs to deliver the R3 cert on its own, and while Apache does this somehow, the Jitsi server does not - but I have no idea how to fix that).
I searched the web for topics related to "jitsi missing r3" and found nothing on that.
So, you're saying that the server needs to deliver the R3 cert? I thought the browser would pull them from wherever the cert issuers provide them.
So the question is: Why does Jitsi not deliver the R3 cert. Couldn't find anything in the web on that topic, either. Damn. This should be easy - the install page for Jitsi clearly makes it sound like that, and it used to work fine before I upgraded to Deb 10 a few weeks ago, too.
I've found the issue after reading Certificates – Prosody IM, and it had nothing to do with Jitsi, so asking here was the right place:
I had configured my webserver to deliver the "cert.pem" for SSL connections. That was incorrect. I had to change it to deliver the "fullchain.pem" instead. (And the other sites server by Apache also used that fullchain.cert file, and that's why it worked there)
I guess that have been obvious to anyone knowing anything about configuring a web server