12.2 is not "very" old - at least not from a technical perspective, meaning, we should support this file. It's a bit odd actually if it works in 12.8 but not 13.8. If you can share the NC file with us we can have a look, but if it's large please don't email it, but make it available via Dropbox, Google Drive or similar.
Another simple option to "heal" the file is to read it in 12.8 and save it again. That should make it work in 13.8 - if not, do let us know. To do this, you just need to run this in 12.8:
objects = nlread("oldfile.nc")
for x in objects:
nlsave("newfile.nc", x)