You do know there is a timer in rated mode, right? Otherwise it must either be a technical glitch or the rare problem with more than one solution. If the timer bugs you, go to unrated mode and take as long as you want to solve a problem.
A Tactics Trainer question
It almost certainly means that you have exceeded the time limit, or the point where you still get points for solving the problem. The timer is a colored bar at the bottom of the screen in Tactics Trainer.
I turn the timer off actually so there's no pressure or distraction. But yeah, if you take too long, you can lose points. The reason is that if a 1600 takes an average of 30 seconds to see a particular tactic, and you're rated 1700, but take 4 minutes, clearly you shouldn't be rated higher after that problem.
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I have lost points on Tactics Trainer problems that I have solved correctly. Does anyone know why does this happens? It seems so counterintuitive!