Alex
Is it possible you may have a bad batch as one of the valves we had lasted only 5 minutes, The others lasted only a matter of days until they suffered the same fault as the one displayed in image
We have since ordered some from ebay and all are working fine and are several months old
The answer is I would not know. We buy these in a few 1000 at a time but they are made by a large Italian manufacturing firm probably in batches of 100,000 at a time. If we have one returned to us having failed prematurely, we will usually replace under warranty as long as all parts are returned and are not exhibiting signs of accidental damage. We can then throw these back at the manufacturer.
We have not noticed an increase in failed units. I've got one on a pole that's only a few months old and it's working as well as the ones that are a couple of years old.
Feel free to email me if I can help further.