Another possible explanation is that you don't have enough satellites, normally we see that you mark enough but to me it has happened many times that if I don't have minimum 8 (I think I remember that was the amount) then the images didn't have the correct date. It has always been said that to fly minimum you must have synchronized with 5 satellites, I initially, especially when you change the zone, independently of if you make the calibration, I would leave a little more or check that I have "enough". How many are enough? I think from 8 upwards.
As you know, the satellite positioning unit has to download the satellite map of the area in which it is located. Sometimes it is difficult and therefore until it does not it is a little more difficult to "see" where all the satellites are and "connect" to them.
P.S.: In an Android device, with certain programs, you can force the download of that file with the positioning of the satellites while you have an internet connection. So with the ST16S you can do it, with the H520 I understand that you can't. What I don't know is if that information is transferred from the ST16S to the GPS of the H520.