Garmin recording pre-set workout distance wrong

I have been using the Runna app for marathon training and have the training schedule loaded onto my Forerunner 735XT. Recently, when I've finished the workout e.g. completing the distance and get greeted by an 'End of Workout' screen the recorded run on the Garmin app and Strava app is 0.2 off the completed distance. Does anyone know how to resolve? This is not the first time I have had issues with distance inaccuracies but I didn't think it would happen for a pre-set distance!