MOV failed due to lighting or OV on power line Feeder control
Apparently the box SPD does nothing. The second hypothesis is that there was no lightning strike involved at all. The first MOV1 didn't conduct, neither SPD, only the 2nd MOV2 has conducted because the mains voltage raised to more than 320VAC. And this was not just a 8/20us lightning pulse.
In my opinion, those devices were connected to three phase system 3P+PEN 400VAC and the neutral got missing. Your apparatus got 400VAC, so that's why the MOV2 failed without the other lightning protection. The customer is a liar.