5N2 continually restarts when copying large amount of files

I have a 5D, a mini and a 5N2. For ‘administrative’ reasons I need to copy a few TB of data from the 5D to the 5N2. Copy always starts OK, but anything from 30 minutes to a few hours into the transfer, the 5N2 restarts.

When I am not copying, and using the 5N2 for some normal data, and Time machine (3 shares) it is stable, and remains up for weeks at a time. The problem is only when copying large amounts of files.

iMac 27" (late 2014) running Mojave
5D attached with Thunderbolt 2
5N2 attached with dual cat 6 ethernet cables to switch, which is connected by ethernet to iMac

I’ve already transferred several TB of data from 5D to the Mini with no issue.

I am stumped

I had this issue, so far seems it was a firmware problem. Try 4.2.2.