External disk appears on new ATV but not ATV2 flashback...

Bizarre problem that has me a bit baffled… I have 2 ATVs (a new one and my trusty 2nd gen ATV2), both pointing at the same external hard drive attached by USB to a MacMini. The new one shows the external drive when connected by either AFP or SMB. The old one however, does not… either directly when I’m at the top-level menu (which is where I expect to see it) or when I dig down into the “Volumes” folder on the MacMini drive.

My guess is that I made the rookie mistake of upgrading the external hard drive to APFS and the old ATV2 can’t see it as such… might that be the case? And if so, am I SOL? Or is there a solve for that?

And if that’s not the case, what could it be? Thanks, guys.