Bubbles from return lines only when Jandy valve is not 50/50

My pump setup is quite simple with a skimmer line and a suction port line that are met at this very old Jandy 3 way valve then goes to the pump. I always run it at 50/50 distribution and have no troubles but since I got a new cleaner yesterday that requires a bit more suction I gave the suction port about 70% opening with the skimmer 30% opening. That was when I start seeing bubbles from the return lines, as well as pool pump not holding prime any longer when the pump was not running, would it be safe to assume the Jandy valve was the culprit?