As I said mediasoup does NOT support FEC for video codecs.
Can you point to the corresponding documentation in mediasoup API?
Because, as I said, Chrome will limit the bitrate/resolution/frame-rate of its sending video stream based on network uplink quality.
You should also describe whether you are testing this in localhost or in a real server, and whether you are consuming the video in a browser running in the same or different computer in which you are applying such a 20% uplink packet loss.