In 2017 fall I bought a Garmin 2D Charlie, an aviation version of Fênix 5X. All worked fine, but somewhere between 11/29/2017 and 12/01/2017 the temperature during my running graphs were no longer there.
Some friends that own the Fenix 5 didn’t had same issue. Friends with D2, in other hand, all missed temperature data. The file is the same, Garmin system still shows it.
So, probably is only matter of “turn it on” to D2 Charlie users. Or, maybe not?