External drive dismounting in Sequoia 15.7 (and previous iterations)

I have been having issues with a new external drive dismounting on my recently purchased MBP M4 running Sequoia 15.7 (and previous iterations).  I wanted to add an APFS formatted RAID to my historic HFS+ RAIDS.  The new RAID repeatedly dismounts, corrupting these data and or the encryption.

Details: The new RAID in question is a Lacie v2 2 big thunderbolt Dock; formatted in APFS encrypted, mirrored and partitioned into two containers for time machine and data volumes. The Lacie RAID drive is under warranty.  Seagate have been genuinely helpful.  But this is now the third RAID under warranty in five-months.  I’ve not experienced reliability issues like this since system 7.   Seagate firmware checks as up to date.  The dismounts have happened in 'safe mode' as well. Sometimes dismounts  show the “temperature critical or fan absent’ warning but mostly not.   Odd thing is that I have two very reliable Lacie v1 2 big thunderbolt Docks that are not affected on the same T3 daisy chain; these older drives are formatted in HFS+.   Hence I don’t think it can be cables etc.  The RAID mirroring was done with Seagate Toolkit, all other formatting was done with Disk Utilities.   It has been suggested that I try reformatting the RAID into JBOD so that Time Machine is on a dedicated drive; but then I loose the mirroring redundancy.  I am at a loss at this point if it is hardware, firmware or software? Any suggestions would be warmly welcomed... 

I have also tested Tahoe on an external bootable SSD; all my external drives mount.  Should I roll the dice and install Tahoe in the hope it handles my external drives better as some claim?