I have an HDPVR2 connected to Linux. When I load a recording into Avidemux it is bot working correctly. Moving the video it will jump 10, sometimes 30 seconds. When I had the PVR hooked up a Windows PC, Avidemux would load the video correctly and it would edit fine. I downloaded a trial of VideoRedo and the Linux recording did fine there, no errors.
https://drive.google.com/file/d/1pDG6Rbyno7sQVGEM8Bvz08RH5V0LO4D1/view?usp=sharing (https://drive.google.com/file/d/1pDG6Rbyno7sQVGEM8Bvz08RH5V0LO4D1/view?usp=sharing)
It is up to the HDPVR2 driver or userspace application to set the max GOP length to your liking (you seem to prefer shorter GOPs for better seek granularity at the expense of compression level). There is nothing Avidemux can do here until you reencode the stream with shorter intervals between IDR frames.