Why did the Legrand light switch stop working?

In stock Legrand switch. Normal connection. Worked ok - the lamp switch. At some point I stopped turning it on. I changed it to a worker (checked, because I removed it from the next room) - there is no inclusion. I remove the switch and connect the three contacts - there is an inclusion (although it does not turn on immediately, but with some kind of full contact of the contacts). Help, what is the problem and how to solve?