Mileage Discrepancy: Map My Run vs. Apple Workouts

I use MapMyRun on my Apple Watch to track my walks and runs. Within the past maybe month, I’m noticing that Apple Workouts has stopped just pulling in the data from MapMyRun and instead is somehow changing that data at will.

Today, my 1.04mi dog walk on MapMyRun was recorded as a 0.95mi walk when it showed up (with the MapMyRun icon) as a workout on Apple Workouts. Yesterday, the 4.02mi run got re-translated to a 3.95mi run. Often, it will show the heart rate tracking, calories, and even the route map but record 0mi for a walk/run.

There is no way to correct Apple Workouts (to my knowledge). I’ve checked apps and operating systems...all up to date. Any reason why Apple Workouts would alter data coming in from another app and suggestions what to do about it?