Could be aging or defective missiles.

How are they stored? How old are they? Is there corrective or preventative maintenence for these missiles? What is the failure rate over the lifetime of the munitions? How many have failed so far and are they in acceptable limits proposed by the manufacturer? Are we seeing a rate of failure higher than average? Is the launcher itself defective in some way as to damage the missile, impacting its ability to fly? Missile software issues? What type of seeker does it use, and can that be either jammed or is it defective?

Hacking a missile system sounds interesting and exciting and dramatic, but a system like this is probably not hooked up to any kind of network requiring internet access. Jamming is more likely, but doesn't make a whole lot of sense for individual missiles in a salvo to fail to jamming. It's my opinion that it's probably just old missiles failing as they age.

I believe we are seeing more failures simply because they are firing more missiles, and I believe we will continue to see these catastrophic* failures as the war goes on.

*catastrophic in the sense that any missile that flies back into the area it is launched from is the exact opposite outcome you'd expect from any missile system.