Not sure :/
I have the same issue. I still have milk as when I squeeze it's coming but the pump just isn't getting it out. Very annoying 😩
Check the size of the shield. I find with Elvie if you use the wrong size it massively affects how much you can pump
I had a problem with it too but discovered an air noise as if it’s leaking. Is yours making the same noise? I’m contacting them today, far too expensive to not work! And it’s not me as I’m expressing fine with the manual pump!