Jicofo - crash after about 30 minutes (OutOfMemory error)

I installed jitsi on a fresh VM with Ubuntu 18.04.4 LTS (8GB RAM) , normal installation (JDK, ngings, jitsi-meet)
First everything looked OK, but two users can’t connect together. After some investigation (Google) I added to /etc/systemd/system.conf
DefaultLimitNOFILE=65000
DefaultLimitNPROC=65000
DefaultTasksMax=65000

Then everything was OK, first conferences (for testing with 4 connections) worked fine. But after about 30 mintes I got error messages and it was not working any longer. Looking into the log files I found in jicofo.log:
java.lang.OutOfMemoryError: unable to create new native thread
every 20 seconds

This occures allways, 30 minutes after a reboot I got these messages, also without any connection.

Looking with "ps -o thcount " I saw, that every few seconds a new thread is created. When 259 threads were reached, the error message occurs.

Has anyone an idea what could be wrong (why is a new thread created every few seconds)?

Dieter

No ideas?