This actually comes up pretty often with motion sensors and its usually down to a few things. The twins can be a bit sneaky since they have this decoy ghost that messes with stuff but wont trigger the sensors, which threw me off the first few times i encountered them. Sometimes its just the ghost being unpredictable with their movement patterns, and they might avoid your sensors completely even if youre sure youve got the right spot

I've found that placement is super important, and sometimes you gotta try different spots on the walls to get them working right. There are these weird dead zones that sensors just dont like, especially after updates. The other thing to keep in mind is that both living and dead players can trigger these things too, so if youre getting a lot of activity it might not actually be the ghost youre picking up

A tip that works for me is using the sensors together with other equipment like emf or temp readings, since that way you know for sure if the ghost is actually around. I usually try to spread them out a bit, putting some inside the ghost room and a couple nearby, that way you can catch them even if theyre being tricky with their movement