The driveshaft CV joint with the failed bolts has been looked at and it appears that 3 bolts backed off and when it "let go" two more bolts sheared, leaving one bolt in place. Obviously one bolt was never going to hold and it failed.

The last bolt is pictured and it has sheared and well as suffered a lot of distortion.

I have now replaced all of the lobro bolts and thread locked and torqued them up. I cannot source a drilled head version of the bolt and being 12.9 they are quite resistant to being drilled.

I have made a recurring note to check all the driveline bolts (including the diff/prop and the prop adapter) for tightness every week if I have used the car.