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?