I was replacing a light fixture at my sister-in-law's house which was controlled by two 3-way switches. With the light removed and the circuit breaker ON the voltage measured at the wires to be connected to the light were 120 volts in the ON position and 40 volts in the OFF position. (Measured with a digital meter) After the light was installed I didn't measure the voltage again but the light worked as expected. When the switches are off the light is completely off. If the 40 volts was "real", I think the light would have a dim glow.

The light works but where did the 40 volts come from?

I think that it may be going through bulb element to your meter?
Unscrew bult and if Zero volts then that was the case. If not,
May be some resistance in switch, removing switch will confirm.
Digitals can be sensitive.

When I measured the 40 volts, the fixture was removed. I could go back and measure again with the light bulb removed. I think it will be the same as with the fixture removed. I drew the circuit out and have been looking at it. It is either leaking through the switch or if the cable is run near another cable which is a live circuit, maybe the voltage is being induced into the one I'm measuring.