Calculations performed on the server (XO) after an activity is uploaded are more robust than what a data field can accomplish. Differences are to be expected especially to Focus but in your case the resume function undoubtedly skews the results as those are very long gaps being recorded within one activity. You may be better off saving as separate activities.
Moving time isn’t a function of Xert’s model. Pauses during an activity are considered RIB that factor into MPA and Difficulty calculations.
Related threads –
Xert Only Counts Elapsed Time - Support - Xert Community Forum (xertonline.com)
Ride time v elapsed time from garmin to Xert - Support - Xert Community Forum (xertonline.com)