Maybe the spring that pushes the plunger is a bit weak. What size needle are you using? If it's 34 or 32 gauge you might try a 31 instead. The tiny opening on the finer needles could be making it hard for the liquid to exit.
I'm wondering what might be off with this version one. It worked without issues for a month or two. I tried using it for five units daily but nothing comes out until I set it to ten, and even then the liquid comes out extremely slowly. Sorry if this has come up before.