make RecyclerView's height to "wrap_content" in Constraint layout
i had the same issue and i find this solution: you should add this attribute to your recyclerview and it makes your recyclerview wrap_content in the constraint_layout:
app:layout_constraintHeight_default="wrap"
let me know if this solution fixed your problem.
EDIT : recycler's height should be 0dp.
EDIT 2 : in the newer versions of support library, use this code:
android:layout_height="wrap_content"
app:layout_constrainedHeight="true"
app:layout_constraintHeight_default="wrap"
is deprecated in newer versions of the Support library, so consider using
android:layout_height="wrap_content"
app:layout_constrainedHeight="true"
instead.