WD RAID to WD RAID - 2TB taking 1 Day + to Transfer

I just bought a new 12TB WD DUO in RAID 0.

I’m trying to transfer 2TB over and all I’m getting are speeds of 10 - 40 MB/s.

Connected via USB3. Both drives test at 300 MB/s + when tested elsewhere, but I when I actually go to transfer it’s annoyingly slow.

I’m on Windows 10, one is ExFAT, other is Mac Formatted but readable due to a piece of software (keep in mind speed tests are giving me 300 MB/S +).

Very frustrated.