I had this same thing happen two weeks ago. There is a shorter segment near my house and the KOM was 51 seconds. Its a bike path right next to a road. The road was closed one morning for road work and I was riding early. I rode on the street for the 1/4 segment and did it in 49 seconds according to my Garmin but Strava said it was 52 seconds....I was kind of mad that I didn't get the KOM. Strava is just its own worst enemy sometimes.