Whatever it is, it isn't mSATA-specific, because I'm posting from a 5.8-stable system booted from and running on an mSATA connected drive at the moment.
Code:
sd1 at scsibus1 targ 2 lun 0: <ATA, TS32GMSA370, N112> SCSI3 0/direct fixed t10.ATA_TS32GMSA370_C528390021_
sd1: 30533MB, 512 bytes/sector, 62533296 sectors, thin
There's something else in the hardware/BIOS event-chain involved with this particular problem. mSATA is a contributing factor, perhaps, but is not the root cause.