ok now i know what its doing i can tell you what to check
it fires the first shot so the cocking lug is ok, first thing to check is the cocking rod, unscrew it completely and remove it from the marker, check the threads are ok, then carefully screw it all the way back in and test the marker again..........its not uncommon for people to put them back in wrong and it feels like its in ok but it isnt...........one of our new team markers was doing the same thing the other day and it was fixed by just removing the cocking rond and putting it back in.
if that doesnt cure it then the next question is, have you adjusted ANYTHING on the marker, ie the trigger/timing or the front reg. its also quite likely that the trigger adjustment can limit the 3 way and stop the marker recocking