Thunderbolt NVMe RAID Enclosure Randomly Unmounting

I have a Mac Studio M1 Max 64GB running Sonoma 14.2.1 (upgraded from Monterey today). It has two older 12TB G-RAID TB2 enclosures (one is used as a backup clone of the other) connected to one of the Thunderbolt busses via an Apple TB2 to TB3 adapter. I am in the process of replacing these with a Startech Thunderbolt 3 4 bay NVMe enclosure with 4 x Crucial P3 Plus 4TB SSDs in RAID 1+0, mirrored and striped using the Apple RAID Assistant. The enclosure is powered with its own 75W supply.

The RAID volume works fine but randomly unmounts for no apparent reason, sometimes when idle and sometimes when reading / writing data, and it does not show the "Disk not ejected properly" message. The enclosure still shows up as connected in System Information, and in the Disk Utility you can see all the member drives but the RAID volume is unmounted. Likewise, DriveDX shows the member drives when the RAID volume is unmounted so they are still all connected. I can remount the RAID volume from Disk Utility. All sleep settings are disabled.

There is nothing wrong with the enclosure, cable or drives as it does not exhibit this behaviour on my i9 Intel 2019 16" MacBook Pro, it stays connected all the time. Interestingly - and disappointedly - it has much faster writes on the MacBook (tested with Blackmagic Disk Speed Test), 1,250MB/s vs 830MB/s on the Mac Studio, although both read at 2,500MB/s. I have also tried a different TB3 cable but no difference.

Any ideas? I have worked with Macs since the 90s so I know my way around them, but this has got me stumped. If I can't find a solution then I'll have to send the enclosure back as it's no use to me, it will be used as my main drive for Lightroom photo editing / image storage and video storage and editing with FCPX. I am also surprised at the speed difference between the devices, I would have thought the Mac Studio would perform better, not sure where the bottleneck is or what is causing the significant difference of 420MB/s.