I don't think it's bolt stick, i think one of your o-rings is leaking, and you gun is 'uncharging' while you gun is sitting. To test this, you can shoot your marker, then wait 10 seconds, then fire across the chrono, and note the velocity, then fire a few shots, and wait 20 seconds, rechrono, and see if the velocity drops.
I don't think it's a bad idea to do a complete o-ring rebuild every few months. Remember, with a matrix, it's either dirt in the reg, a nicked o-ring, or the battery.
Good luck, please let us know how you solve this.