Thanks for the quick reply! It is iOS10 on an iPhone 6 Plus. These are the buttons below the file/folder list. I have not had iOS10 long enough to see a pattern. It is difficult because it happens only occasionally, so it may be a while before someone else reports, plus it is just a nuisance since you can solve it by restarting the app
This is Textastic version 5.3.1. Have not purchased 6.
Customer support service by UserEcho