It is multistage and certainly not cheap.
It did not fully actuate and when robot submarines tried to manual actuate it has not shut off the flow.
My personal speculation is that it nearly closed, but not completely. The flow rate from the well is only 29 gpm, or about 3 garden hoses. It seems to me that it is partial shut off.
Do they know why the BOP failed to actuate? I worked on a Transocean rig years ago and we had a BOP guy that thoroughly tested the BOP before it was used. That's all he did, work on that BOP, making sure it was working right.
Covered under warranty