It sounds like it's my fault -- I made some changes to the USB code recently and there's been a lot of breakage, this is probably one of those cases. I don't have an iPod 6G, but if you don't mind testing a few builds I should be able to fix it.
First make sure you have "USB Mode" set to Mass Storage and not Ask. Ask mode is completely broken for the time being.
If that does not resolve the problem, install this debug build to your ipod:
https://drive.google.com/file/d/1ubf5E-KDFGJ9G-JvVswHxk3KO8jwC0IO/view?usp=sharing. You can simply unzip it to the ipod's disk after deleting/renaming your old .rockbox folder. Boot into Rockbox, connect to your computer with HID mode enabled, wait about one minute and then unplug it. Go to System > Debug > Dump Log File to dump the debug logs. The log is written to a timestamped file,
logf_YYYYMMDDHHMMSS.txt in the
.rockbox directory. Upload the log file here and I can take a look at it, hopefully it will reveal what's wrong.