Hi Helen, yes we were very very unlucky, and the first time breeder was also heartbroken over the loss of her other 2 pups. As you say, a high COI does not by itself mean problems will occur, but can increase the risk and may have done so in this case. I have chosen a fieldie now despite the breed having a COI of around 20. Of course a lower COI would have been preferable but wasn't an option. However I am sure of the health and temperament of both parents and grandparents (and other relatives) and have complete confidence in the breeder.
I will have another cocker, they are my first love, but I will do my research more carefully than last time.