photos archive will not copy

my problem:

on my wife's mac mini (2012, mojave), the archive file of photos is on an external firewire HD, it is 120GB large. i want to transfer this file back to the internal SSD.

if i try to copy it directly, copying gets very slow after 89GB, then after a long time (30min?), an error message displays saying 'some files cannot be read or written' and copying is aborted.

i zipped the file, then copying from external HD to internal SSD of mac mini works. but on unzipping (with mac software or unarchiver, on desktop or in pictures folder), the unzipped file cannot be saved, error -1 saying 'not the permissions necessary'. read and write permission in all folders are correct (via command i info).

disk utility's first aid did not help. repair by onyx did not help.

i tried copying and unzipping on an empty user with admin rights. problem remained.

i erased the mac mini completely and rebuilt it via time machine backup. problem remained.

BUT: to check, i copied the zipped file onto my mac pro (2013, mojave). here, the file unzips without problems. hmmm ...

any ideas how to get the archive file onto the mac mini?