i'm using an ipod nano as well as an older 80 gb (hard disk drive-containing) ipod on an up-to-date macbook air.
itunes, and now the music app, have long seemed to be confused by my use of two ipods, because i would inconsistently find, on plugging one in to sync via usb, that it was being treated like an ipod associated with some other music library. it would forget its sync setting (sync music, only some playlists etc. rather than all) and be effectively unusable via the syncing interface until its contents were rewritten. that is annoying enough, but this also prevents it from syncing playcount information, which becomes lost upon rewriting contents.
as i said, this behavior was inconsistent for me and i generally sync one ipod more often than another, where i did not notice the behavior on the more frequently synced one, so i assumed it had to do with one ipod becoming treated like a primary sync device and the other one losing status.
however, the behavior seems to have become constant upon upgrading to macos catalina, and i have no idea what to do to fix it. an error message i got from the finder sync interface suggested that the computer literally thinks the ipod's associated music library is not the one i am trying to sync from (on my macbook), but even if this is so i don't know what can be done about it. (could a corrupted library be the problem? but my library is now brand new thanks to the itunes->music app switchover.)
any advice? the internet seems strangely silent on a problem i have always supposed was not uncommon.