If suddenly your power changes dramatically on your watch or iPhone while running at the same pace, or power is off when you upload your data with the Stryd app on your phone, likely the weight setting on your Stryd changed.
To address this problem, you can update your height and weight on your Stryd with the Stryd app. It is recommend to actually change the values when updating your height and weight (do it twice to go back to the original value).
Note that it is currently not possible to recalculate power of runs with incorrect data.
If you need further assistance, contact email@example.com.