Fenix 5X paired, syncing, but no activities are shown

Fenix is correctly paired with my iPhone, showing the green dot, notifications works properly, but after a long syncing process no activities are shown.
Tried several times to unpair and re-pair, turn on and off both phone and fenix; had also a factory and after it syncing worked properly but just for a few times.
Software is updated.

If I connect the Fenix through garmin express or via wifi, everything works good.