Very-high (abnormal) CPU utilization after upgrading from 10.2.16 to 10.3.9 (latest)

After upgrading MariaDB from 10.2.16 to 10.3.9 (latest) via the official MariaDB Debian repository we are seeing very high cpu-utilization even if SHOW PROCESSLIST shows no or only very little query activity.

While the CPU usage is perfectly fine after restarting the MariaDB demon, the CPU utilization continuously increases after some 5-10 minutes until it exhausts all of the VM's CPU cores. After a few hours the MariaDB-VM even almost kills our whole VMWare ESXi host equipped with Dual Xeon v4 12-core processors. We did not have any similiar issues with MariaDB 10.2.x.