See your emulator, your ADB communication probably failed, open your terminal and check that your emulator is displayed with an ADB device, generate a new RSA certificate and try again, I recently had the same problem with debugger from IDA and its competitor JEB, and that was the solution that worked for me.
See also how to properly configure the ADB for ...
It's possible that the kernel is not actually gzip compressed but uses another algorithm. I would recommend using vmlinux-to-elf which can not only automatically detect the compressed stream, uncompress, and convert to an ELF but also parse the kallsyms tables and symbolize the image.
You have two possible approaches in here:
Analyze the APK of the device, reverse engineer it and try to make sense of how it communicates with the USB device.
Connect the USB device to a computer, sniff the USB packets, and try to make sense of how it communicates with the host.
I believe the former would be straightforward and simpler than the latter, not ...
It required a minor patch in ffmpeg because the mjpeg format used by this type of cameras is not fully compliant with the standard FF DD [Restart interval] JPEG marker.
It was solved by "cehoyos". See details at https://trac.ffmpeg.org/ticket/8211
This solution applies to the cameras used in some wifi-rc-tanks, a few cheap drones ...