I figured that you were using instance attached NVMe's since you mentioned the scale of your load – an EBS even with the io2 Express storage class can't keep up

I figured that you were using instance attached NVMe's since you mentioned the scale of your load – an EBS even with the io2 Express storage class can't keep up with a physical NVMe drive on high intensity I/O tasks. Regardless, AWS takes care the hardware cycling / migration in either case.