Fortunately, I couldn’t determine the behavior of the Jolla 1 and Xperia X.
Sometimes the network was gone due to poor reception in a building, for example. But that could usually be solved via the SF utilities and “restart network” or via “restart ofono” etc. without a complete reboot.
Same here on Sailfish Xperia X - when crossing borders occasionally it happens, but I had just to press the OK and everything goes on normally.