10.13.3 - RAID Can Read but Ejects when Trying to Write

Hi All

So I'm in a bit of a conundrum...I have a brand new iMac Pro (whoohoo!) that I can't use ($%@%) because of a real head scratching RAID issue.

I have a 12TB ProAvio RAID enclosure set to RAID 0. 10TB out of 12TB used. USB 2 connection and FW 800. All current firmware and updates.

Works flawlessly and has for 2+yrs on my Mac Pro 10.12.4.

Now, on the iMac Pro 10.13.3 it works...but not really. I can read all day from it no matter what connection, USB-USB, FW800/TB2adapter/USBCadapter or USB/USBC adapter....BUT....Trying to write USB-USB ejects the RAID and I have to power cycle the array...Here's what I have found broken down by connection.

USB-USB

Here's the worst part. I really need the speed of USB2. On my MacPro I was USB-USB and getting a read/write speed of 240MB/Sec. On the iMacPro, as I said above, I can read as much as I want, try to write and it knocks the RAID offline. I have a BlackMagicDesign disc speed test and when I run it with the USB-USB connection, I get 250MB/sec for maybe 2 seconds then it knocks the RAID offline. If I try to write any file to the RAID...it gets knocked offline and I have to power cycle to get it to connect again.

USB-USBC adapter

This connection works. With a small USB/USB-C adapter I can read and write. BUT when I run a speed test I get maybe 30MB/s. Far below what it should be getting and in video editing...there's no way this will work.

Firewire800-TB2-USB-C Adapter

This connection works as well. Granted it's through two adapters to step up from FW800. BUT according to speed test I'm in the 30-40MB/s range again.

I'm seriously confused as to why it's not working at all to "kinda" working in other situations...and the fact that it even starts by saying it's 250MB/s before getting knocked offline with the standard USB connection.

Apple has told me they don't support it...but the fact that it works fine on my Mac Pro and not with my new $8000 iMac, leads me to believe it has to be something with the change from Sierra to High Sierra.

Does anyone have any suggestions or ideas? Thanks so much!!

**note - I DO have the "put hard drives to sleep" etc etc turned off.