I found that some additives react to this skimmer. For instance those anti-chlorine additivies with slime protection made my skimmer go wild.You can also unscrew the spray injector to see anything choke there.
Check your pump whether there's anything wrong cos the pump flowrate is important to drive the injector.
Sometime when i do maintenance and switch on and off the pump the bubble count seems drop so i just did a couple of switching on and off then its back to normal again. Probably some airlock as i don't have any check valve. After getting back the bubbles make sure you set the level to the correct one(should be below the transparent reaction chamber or else you risk overflow)
Last thing i encounter is that if the outlet pipe is into the water the foam level drop. I guess is because of backpressure. So if you place it in sump the water level is important.
That's all i can think of.