I track my steps with my iPhone 6 Plus, with latest iOS and app versions.
I tend to rack steps up slowly, due to health issues. The last time I checked my step count, about a week ago, I had just over 19k steps. When opened the app tonight, I noticed my step meter looked low, so I went to check my step count...and I have just over 10k. I was saving for 30k, I did not buy anything...yet 9k, plus the 5-6k I earned this week, are GONE.
Due to said health problems (multiple disabilities) I've basically lost about 3 weeks worth of steps. No other progress seems to be missing, but this is still hugely frustrating!!