Cannot update ipod classic

I recently updated to Big Sur 11.5.1 on a mid-2014 Macbook Pro. Since then I haven't been able to update my iPod Classic and in fact something happened which caused all my music to be wiped from the iPod.

When I connect my iPod appears in Finder and if I go to System Info, it also shows there - however it gets to a point where Software: Loading.... appears in Finder and it then hangs indefinitely - I've had it connected like this for several hours and nothing happens.

If I try to eject, it won't let me, so I've ended up shutting down the Mac and then removing the cable - after I did that once, I noticed all my music had gone, but apart from that the iPod itself looks fine. I've reset the iPod a few times (Menu/centre button), but that hasn't changed anything. I should note that my music lives on an external USB drive, but that's never caused update problems before.

Any ideas? Not sure if it's the Big Sur update, or an iPod error or something else.

I know the iPod classic is old news, but I'd like to keep it going if I can.

Thanks in advance.