looks like a time zone issue,
but I have a question, does it affects progression chart graphs? values on chart calculated based on hours (or minutes or days) between trainings?
p.s. attached image with my activities, file name is actual date and time in my time zone, activity date is wrong for each training Screen Shot 2017-02-20 at 15
You can update your Timezone using Account Settings / Advanced. Let us know if this doesn’t resolve your issue. (You may need to re-import your activity).
for all activities was the same time zone, but time difference is not constant, from 1 hour to half day, but original question is more important for me to understand accuracy of calculations
Calculations are based on seconds between workouts.
for new uploads there is the same issue here, no matching date and time for activity 
