This problem happens if the conditioner is too thick or if the water supply to the conditioner compartment is not sufficient . If you are using a thick conditioner, try to change it for a less-dense conditioner.
If the water holes that allow water into the fabric conditioner compartment are clogged, you need to manually clean them. For this, first, take out the soap drawer. Now, locate the holes seen above the compartments of the dispenser drawer, and then clean it using a rigid bristle-type brush. Give special attention to the small holes seen directly above the fabric conditioner's location. Thorough cleaning using the brush will solve the problem.
This water channel usually gets clogged by a mould formed by a type of black/brown bacteria, which prevents the water from flowing down to the fabric cavity. Also, make sure to spray the cavity and the areas near the holes using an antibacterial spray. This will inhibit the growth of black/brown bacteria.