@MccG I don't work for Fitbit, i'm just a frustrated fitbit user like you, but i want to make sure you have the right information. I'm primarily an iphone user so bear with me if my android terms are a little off
1. In regards to you having a phone that's not supported it shouldn't be an issue. As long as your phone is running at least android 7. So your phone would have to at least be running nougat, oreo, or pie. If you are running marshmallow or below you could have an issue which i'll explain way at the bottom.
2. There seems to be an issue with the charge 3 and having the wrong time zone selected and the time not being accurate. https://community.fitbit.com/t5/Charge-3/Charge-3-is-showing-wrong-time/td-p/3367615 and https://community.fitbit.com/t5/Charge-3/Charge-3-showing-incorrect-time/td-p/3118456
2a. This might shed some light onto why you are seeing that weird behavior in those sleep patterns. It could also explain why you aren't seeing data on the phone and having to reinstall the app. I initially started using fitbit with Windows phone and it had that time zone issue (i used to travel for work). There was weird stuff going on when the the time zone changed. When it jumped forward i had a gap in data, but when it went backwards i lost data and nothing would display. It ended up with me having fitbit reset my account, but that was back in 2014.
3. Tracked distance can vary and depends on what you are doing even though its the same route.
3a. Are you texting while exercising? if so your arm isn't getting that full range of motion and you won't get credit for steps.
3b. If you notice when you are pushing a shopping cart you don't get credit for every step. This kind of explains what happens when you are texting, but could also be true if you are holding your phone to your ear while on a phone call and the tracker is on that hand.
3c. Are you mapping your run? Fitbit hasn't provided a definitive answer on this yet, the but i think its counting your charge 3 and your phone as a tracker (my guess is the connected gps wasn't implemented correctly), which means that you are now using 2 devices at once and fitbit will take the data from those two devices and merge it into one data set.
Now if your phone is on marshmellow or below you can run into issues as things change with each new release (its true for the iphone too). New dependencies can be added to android just like some can be removed. If fitbit based part of the app on something that was available in marshmallow, but it was removed in nougat Fitbit has to change the feature to make it work. Not every phone is eligible for every OS update so as bugs are fixed in the app you won't be able to benefit from the fixes. Google should let you have the last stable release of the fitbit app for marshmallow, but if fitbit didn't catch the error affecting your tracker until nougat your out of luck.
I wouldn't accept being told your mobile device isn't on the approved list as an answer if you're on at least android 7!
