I am having exactly the same issue with Runtastic Pro on my 950 running fast-ring Insider Update. I keep hoping it will work as the new versions are rolled out, and still no joy. Because it isn't updating, it shows as Pending on the phone. It still works on my 950XL, which I kept on release preview. I just updated the 950XL two days ago, and it didn't break Runtastic Pro. I have sent several emails to Runtastic Pro without an answer.