Activity Distance Measurement changed after phone reset last week.

I have been walking the same route almost every day for the past several years. The distance of the route is 3.75 miles. Last week, I was having problems with my watch as I was not hearing text notification sounds. I worked with two techs on the phone and one had me reset my phone and that totally screwed up my watch and I had to go into the store to work with the Genius Bar. The tech was great and got the watch and phone to work However, I noticed on my walks now which are the same route, my distance on my watch is only showing 3.36 miles. Does anyone have any idea what could have changed? Thank you very much.