The shoes I purchased are Lake's. But I have had the same problem with Shimano. They both came apart at the heel. The sole broke away from the shoe. Maybe I do walk around to much.
I ride about 4000 miles a year and I am sixty-seven years old. So, I know I will never get much faster. I riding friend of mine is seventy-four and he will average around 17 with clips. I think he does well.