Same thing happened to me sadly . I went to vacation for a week at a very humidy place and suddenly the button stopped working.

Although the button presses perfectly it doesn't lock or shut down the phone. Been using the phone like this for a month now and it has started to be really frustrating. I can't turn off my phone now that it cannot be opened without the power button.

Also the same thing happened last year when I went to the same place and a few days later I came back suddenly the button started to function again by itself.

Can this happen because of the humidity of the region? Any suggestions?

I really need help .