First, make sure you are using the correct mobo plain RGB header. The case certainly appears to have fans with plain RGB lights, and NOT the Addressable RGB type of lights. Your mobo has both types of header (2 of each). The plain RGB headers are the ones with FOUR pins, not the 3-pin ones.
The case comes with a three-headed RGB Splitter cable so you can connect the lighting cables from all three supplied fans to a single mobo plain RGB header. Are you using that Splitter cable? Have you tried using both of the plain RGB headers? See your manual, p. 1-2, items #5, at top front and bottom front.