Booking hotels through Hotels.com App Cheaper Than Website?

I’m booking a hotel and i always use hotels.com. I was checking it via website and then later on my phone with hotels.com mobile app… however i noticed the rates were a bit cheaper on the mobile app. Is there a reason for that? It showed 18 percent off discount on website but through mobile app, it shows 20 percent.
Also i use fatwallet when booking through hotels.com to get cashback. However, if im using the hotels.com mobile app, does that mean i can’t get cashback?