More likely it means that they are having connection problems - engine use in the way you describe is actually one of the easiest forms to detect, and they will get caught & banned very shortly if they are indeed using an engine.
using engines?
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I thought it might mean that the player (opposition player in the case of the person reading the timer) had exited the game screen or app.
I have had a couple of instances where I have been winning a 10min game (only by a few pieces) and the timer come up and goes on and off a number of times for 2-6 mins. At this time my opponent seems to start playing really well.
This does not seem to happen in shorter games, which is why I think these people are exiting the app and using an engine, their game play changes too much....
I have messaged my opponents and asked them directly and they did not respond.
I have no direct issue with loosing. I just post this as I don't like thinking I am being cheated of my time. If I wanted to play a computer I would not use this app.