ios – Something keeping my iPhone awake

For the past week or so, perhaps since updating my iPhone 6S to iOS 14.4.1 or 14.4.2 periodically if I plug my phone in to charge, or even just raise to wake, whether I fully wake it with TouchID or not, then it does not go back to sleep, whether charging or not.
The screen stays on indefinitely. I’ve tested it to 15 minutes which is far beyond normal behaviour for either raise to wake or its set sleep period when fully woken.

I am not actively running any app designed to keep it awake, like a sat nav etc.

This may coincide with the iOS update itself, or with the series of app updates I tend to run only infrequently, usually after an OS update.

I have discovered if I swipe up to kill ‘some’ apps this behaviour stops. I did this at “almost smart random”, killing a 3rd party app I knew had been recently updated then re-testing until it stopped misbehaving. I didn’t write down what order, rather annoyingly, hence the ‘almost’ smart. My current suspects are IMDB, AnyList & Virgin TV Control. A reboot will also reset the behaviour, though as this is in effect rebooting all the apps it seems less useful as a diagnostic. Once it behaves again it may take up to a couple of days to manifest once more, so this is tough to tie down.

As I doubt there are too many people who have this issue and all three of those apps, this is really a “has anyone else had this issue & can we jointly discover any commonalities?”