Nextcloud Client 3.0 slower that 2.6

Hi, I am using NC 19.0.4 on Debian Linux, and the Desktop Client on Windows 10 x64. My Nextcloud Client is synchronising about 600 GB in about 100.000 Files.
I now upgraded from Desktop Client 2.6 to 3.0

Unfortunately the sync process is now about 5 times slower than before. I already tried to do some tuning on both Apache Webserver and MySQL Database, but no positive effect. When uninstalling the 3.0 client and using 2.6 again, the sync is as fast as before. Is there anything known why the 3.0 Desktop client is slower?

if there are regressions between version, you can report them to the developers