Jitsi-meet on Debian: conference participants don't see each other – strange memory issues

Hello! I installed jitsi-meet on a Debian / Ubuntu 18 Vserver following the quick install guide.
I can access the service at meet.mydomain.com/sessionname and see my self.
But participants don’t see each other and neither do they see a thumbnail. So it always appears nobody else is on the conference even if two people from two different machines access the same session.

In /var/log/jitsi/jicofo.log the following error is being repeated during the session:

Jicofo 2020-03-24 19:20:27.071 SEVERE: [60] util.UtilActivator.uncaughtException().122 An uncaught exception occurred in thread=Thread[pool-11-thread-1,5,main] and message was: unable to create new native thread
java.lang.OutOfMemoryError: unable to create new native thread
        at java.lang.Thread.start0(Native Method)
        at java.lang.Thread.start(Thread.java:717)
        at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:957)
        at java.util.concurrent.ThreadPoolExecutor.processWorkerExit(ThreadPoolExecutor.java:1025)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
Jicofo 2020-03-24 19:20:33.269 SEVERE: [41] org.jitsi.xmpp.component.ComponentBase.log() Ping timeout for ID: SjtsZ-94
Jicofo 2020-03-24 19:20:33.359 SEVERE: [41] org.jitsi.xmpp.component.ComponentBase.log() Ping timeout for ID: SjtsZ-95

The output of free -h reads like this:

              total        used        free      shared  buff/cache   available
Mem:           8,0G        552M        7,3G         22M        189M        7,4G
Swap:            0B          0B          0B

In /var/log/prosody/prosody.log each new participant joining the conversation produces an entry of the form

Mar 24 19:20:03 mod_bosh        info    New BOSH session, assigned it sid 'e51afbf6-21f6-4ff9-ae3c-fbd5519fdf58'
Mar 24 19:20:03 boshe51afbf6-21f6-4ff9-ae3c-fbd5519fdf58        info    Authenticated as 8b40cec7-c788-4452-916b-0b36922f6530@meet.mydomain.com
Mar 24 19:25:24 bosh65d50eac-027c-4f69-b32b-61d865cab631        info    BOSH client disconnected

I am an experienced Linux user but could not help myself. After two days of debugging I’m now seeking your help. Thanks a lot.

I’m aware of this thread but think my RAM is enough: [Jicofo] Java OutOfMemoryError