Just occasionally the 3G/4G service to my iPad is seen to be up momentarily in the following snapshot of the preceding week taken from AA’s clueless.aa.net.uk; red = dead, faint streaks of yellow+purple show activity.
I have rebooted the iPad and now all appears normal. Before the reboot, the iPad displayed ‘no service’ or ‘no signal’ or some such, and the bar graph at the top rhs was absent. The basestation was up, because other machines were using it on Monday night during the outage.
I’m inclined to blame iOS 13; this has never happened before.