Sounds like the pre-fill valve doesn’t close until 2nd attempt. Be that a sticking valve or loss of clamp lock up signal I’m not sure. Could even be low pump output pressure or flow.
I’d check and confirm pump function, then check for signal to valve, valve for sticking and then maybe pressure loss through manifold. One thing is you don’t have any special modes or options turned on do you? Are you sure the clamp is making high pressure position?
Rick.