When I find a splice that is suspicious but not obviously broken, I will squeeze and jiggle it with my fingers while looking to see if it causes the indicator light on the sensor to turn on or off.  If manipulating the splice causes a flicker or blinking, you have a bad splice that should be repaired.

The wires are twisted together (not very well) in this example , but the same thing can happen if you have a loose connector or wire nut. It is important to note that when you are dealing with the Daisy Chain wiring configuration, you may actually be affecting the sensor on the OPPOSITE side of the garage door, so be sure to look at that one too.