That was a frustrating fix.

The MX Master has a "gesture" button under the rubber where your thumb rests.

I don't believe I ever used it intentionally.

But because it is a gesture button, when it fails the mouse no longer responds as it always thinks it is gesturing.

Pull the wire and it is fine, but diagnosing it is rough.

I feel you. Here in Europe you have to pay around 100 bucks or more to get some decent quality from Logitech. In the past I used mice like the G9 which was build like a tank. Nowadays it's something like a throwawy part, even in the higher price range. Same goes for keyboards, which I tend to build now on own.