When you do 'select all' on the contents of a window, my text editor on the ipad, Textastic, immediately hangs. The Textastic developer kindly explained that this was an iOS bug: what happened was that in settings: accessibility > “speak selection” got turned on and that causes the bug, which stuffs the current app completely. So do watch out. I was completely paralysed by it and never put it down to that accessibility settings change, something which I had tried and then forgotten about, so I never associated it with the sudden appearance of the bug. There had been a new release of Textastic, but in fact that had been too long ago to explain things, but in my panic I made a false association between the two.