Naim Core music library backup. Help!!!!!!!!!! Not a techno guy, not an idiot.

My old library was transferred successfully by a shop from my old Naim UnitiServe to my present Naim Core, so we know it's in FLAC.  I've added substantially to the Naim Core and wish to backup the files and eventually transfer my library to a new Naim Core plus have it all backed up.

I'm using a Seagate 2 TB USB 3.2 Gen 1 SSD.  Because everything is in FLAC, usage is around 600GB in the current library, so more than enough room (2775 CDs).

I've formatted the Seagate to Apple as I use an iPAD.  That's my reasoning.  It formats and off we go.  It shows backup in progress for 41,525 files.  5.5 hours later we are 50% complete.  It finishes, shows success and on the readout shows files to process 0, and files backed up 0.

I've repeated this now 3 times with same result.  All seems well until the end.  What am I missing?  Thank you, thank you, thank you for any insight.