MadDogDeandisable Driver verifier by command prompt.
The laptop came preinstalled with the 2drives in a RAID 0 array - Asus made the decision not me. It is 2x 512GB drives, but show to Windows as a single 1TB drive.
That's why I am replacing these two 512GB SSd with a single 4TB drive.
The UEFI partition was also cloned. Acronis did an excellent job in replicating the drives perfectly on the single 4TB including the UEFI and the Recovery partitions. When Windows booted it just didn't like the setup and gave me the (rather unhelpful) "Stop Code: KERNEL_SECURITY_CHECK_FAILURE" message.
By the way, thanks for your help so far 🙂