I use the ACP delrin bolt but was aware that using the ram also means you have to change pressures for it to function properly - HPR should start around 400psi then tweak from there. Thread below on the topic:
The had also been some ACP bolts that did have a slight roll back issue so the balls would be away from the eyes. If you fire with eyes off and it shoots fine, then that might be the issue. A shim or an extra o-ring would remedy that. Since you stated that the bolt did not seem to go back far enough, this is less likely to be the problem.
Next, did you do a full maintenance on it? Particularly lube the solenoid. If you want to just quick test without removing the solenoid, place a couple drops of oil in the LP hoses (front and back). Cycling the marker should wash the oil over the solenoid. If that worked, then you should take out the noid and clean/lube it.