I've been using Nike+ for at least 5 years too. I understand the need to revamp their app, but NRC was just not ready when it came out. If you want users to spend effort on getting used to a new user experience, you need to offer them something in return. NRC just didn't have anything extra to offer. Not only that, it took out a few features. It's gotten better since though.
On my iPhone6, it's very stable. I just hope it works well on my Apple Watch when it arrives Friday. I bought the watch mainly for the running.