Hi,
Please check if you are able to share a test sample so that we can give it a try. Maybe a test sample like this:
Doesn't work nvv4l2decoder for decoding RTSP in gstreamer + opencv - #3 by DaneLLL
drop-frame-interval is not a runtime-configurable property. For changing the value, you would need to destroy the gstreamer pipeline and re-initialize a new one. Not sure if you are able to re-initialize the pipeline in your use-case.