How old is your Pi? I had the same issues on a generic board (Le Potato) but upgrading to a Pi 4 Model B fixed it for me. I have both my Neptune 2S (modded) and Neptune 3 Pro (stock) running on the same Pi with no issues.
Definitely change your USB cable. If you've got some complex files, maybe the cable can't handle the bandwidth (experienced this back when I was first starting out)