I'm curious about how you introduced and explained the importance of reflection to your students?
I used to have similar issues with reflection papers when I didn't explain much about the process of reflection to them. I've gradually started to add in more explanation of not just the activities, but also discussing why we reflect.
I am still trying to find the right amount of explanation vs. exploration for this, leaving students to just "figure things out" hasn't worked well from my experience with reflections so I would be interested to hear what others have experienced.