I have installed 2 or 3 motion sensor light switches in two different locations in my house and all have failed after a while. They continue to work as regular switches, but the motion-sensitive feature stops working. Could there be any problems with the house wiring that causes this?

No, as long as it was installed per the instructions. The most popular instruction ignored is do not connect when live, shut off the circuit before connecting a device such as this.

Probably just more junk Made in China.

Try using something Made in USA, such as:

Sensor Switch, Inc.

Nice answer mr russell!!