Just to provide an update on this, I am told that the problem seems to be with the power supplied to the mSATA port on the DH87MC motherboard. Apparently the SSD needs power at the higher end of the spec, but the board delivers power at the lower end. So while both devices are in spec, being at opposite extremes there is some resulting unreliability.
Intel have offered to refund my purchase price for the motherboard which is very nice of them, but I'd like to keep the board so I've asked them whether they can refund the SSD instead. I would like to get another device that isn't mSATA and see if I can squash it into my tiny case somewhere so I can keep the Intel motherboard, which was the whole point of this upgrade (wanted Intel onboard video for the open source Linux drivers.)
I would also like to say I wish I could get this level of support from other IT companies! It's nice to deal with a company that really does stand behind their products.