Videos are lagging when playing 2 Video on 2 Screens

[TechG3n]

Hi,
I'm using a Pi4 4GB to display two videos to two Displays
As demo i use https://files.pimylifeup.com/omxplayer/bigbuckbunny_30sclip.mp4.

I have increased the GPU memory to 512MB and the Command looks like
omxplayer -o hdmi -n -1 --display 2 --loop --no-keys --no-osd --pos 00:00:05 -r /home/pi/bigbuckbunny_30sclip.mp4

When i start one instance it runs fine, but if i start both the videos start to lag/hang.
At this point the CPU is at 10%, 3GB free ram, 428Mb free video memory an no temp problem (43°).
I have tried to put the videos on a fast USB Stick, or one on SD and one on Stick.

What can be the problem that the video lags and is there a fix?

[rijotech]

Enable this on your /boot/config.txt
and upgrade your firmware sudo rpi-update

dtoverlay=vc4-fkms-v3d
max_framebuffers=2
gpu_mem=512