Data completely different between fitbit and app

[Midgett]

So when I headed out to ruck this evening, I started my tracking in the Fitbit app and on my Charge 2 simultaneously (I like the mileage call-outs the app gives me through my headphones, and the data that the Charge 2 provides at a glance.) When I got home I stopped them simultaneously. I am getting a huge disparity in stats between my Charge 2 and my app, and when my app syncs the device data, it's different yet again. 

Example, today I got home at 3 miles by my Charge 2, but the app showed 2.9 miles. So I kept rucking until the app showed 3 miles, and my Charge 2 displayed 3.04 miles. I then stopped the app and the Charge. Once the data synced, I had a double entry for my ruck. The app logged the data from my Charge 2 as a separate hike from the data my app logged. Plus, the app data that just said 3 miles logged as only 2.96 miles, and the Charge 2 data that previously displayed as 3.04 miles on the device logged as 3.07 in the app. What's more is there's also a 36 second disparity between my Charge 2 and the app. 

What the heck is going on, and how do I fix it?

[JohnnyRow]

I never tried tracking both ways at the same time but I expect that is why they are logged as different events.  I also wonder if they can both actually start simultaneously or if one has to delay for the other to get started.  Plus not sure I would call 3.04 mi vs. 3.07 mi "completely different".