Thanks for the picture, that's very helpful.
I should have mentioned before, I'm assuming from your other efforts that the cleaner itself, and it's hose, is all clean and free of debris.
Do you have a leaf canister on the cleaner hose, or does the debris picked up by the cleaner end up in the pump strainer basket? The reason I ask is that the suction line dedicated to the cleaner may have become impaired by debris in that line, if the system was working fine in the past. You might want to consider adding a leaf canister if you don't have one. That would provide the same protection that the skimmer basket provides for its suction line.
If that's a possibility, the next thing I would do is open up the electric cleaner valve (remove the actuator, then take out the 8 screws and lift straight up). Then I'd stuff a garden hose down there as far as I can and try to seal around it somehow and force water back toward the pool, with the port held open at the pool, and see if anything comes out.
After being sure that suction line is not fouled, to get more suction coming through the cleaner, to get the rotation speed on the cleaner that you want, try partially closing the two valves beside the cleaner electric valve
