Further notes:
This morning I rebooted Mac and followed what happened: Stuttering in the beginning. After an uptime of 2h 30min reverse video playback worked well, the previous test was with an uptime of 50 mins and at that time the playback was stuttering.
Another reboot and stuttering playback: I connected USB-C SSD to the Mac and started copying files to it. While file copying was performed also the reverse video playback worked well. After the files were copied, stuttering continued.
Has this something to do with PCIe(?) interrupts or what? I would say it is definitely a system level problem.