Pixel distortions when the pipeline's FPS falls below the frame rate of the RTSP sources

Seems you are using the IP camera. Does the camera’s bandwidth support 10 streams on the same port?

Have you follow the instruction in DeepStream SDK FAQ - Intelligent Video Analytics / DeepStream SDK - NVIDIA Developer Forums to set the nvstreammux parameters?

What is your GPU? Can you measure the GPU performance by “nvidia-smi dmon” command when you run the 20 streams case?