Each different platform will use their own standards for moving vs “paused” time.  Each will have a different threshold for when to stop or resume recording around a stop or pause.  Say you go for a run, but then stop to check a message at an intersection.  One platform may take 5 or 10 seconds to acknowledge that you stopped and keep the timer running for that time while another may be more sensitive and stop after just a couple seconds.  Same issue when you resume moving, one may start recording right away while another may wait until you exceed a certain speed before it thinks that you are moving again.  You also have some platforms that will use the moving time only for pace calculations while other platforms will use total elapsed time.  When that happens, you will see the biggest discrepancies.  For the best accuracy, use a dedicated recording device like a sports watch and turn off auto-pause.  If you want only moving time, be diligent and stop and start you watch manually at any “stops” along the workout.  Phones and things like that are never going to be as accurate with their recording.  The other tip would be to be consistent with whatever you use.  Don’t use one app’s pace one day and compare that with the pace from another app the next day.  As long as you use one app all the time, it will give you fairly consistent results even if they are a little faster or slower than your true pace.