Inconsistencies between Garmin built in (Vivoactive 3), SAA through Garmin Watch (Vivoactive 3), and Fitbit (Alta HR)

For kicks, as I was testing out an Alta HR for resale, I wore it, as well as my Garmin watch, and checked each of the results this morning–stock Garmin app, Fitbit app, and SAA, which tracked from my Vivoactive 3. The results have me confused and wondering which is right…

The most glaring inconsistency is deep sleep recorded:
Fitbit: 19%, 1 hr, 36 min
SAA: 59%, 4 hr, 49 min
Garmin: 53 min

The fact that stock Garmin and Fitbit caught that I woke up to take a leak at 5 a.m. and SAA didn’t is inconsistent as well. I’m sure there are other inconsistencies, but what do I make of it all?
SAA:

Fitbit:

Garmin:

I checked both Sleep as Android and Garmin Connect after a sleep this morning. Again, SAA is reporting more than 50% deep sleep, and didn’t capture the fact that I woke up to pee at around 4 am.

I kind of want the money I paid for SAA premium back…