Nearly identical mosfets yet only 1 works (FQP30N06L vs RFP30N06LE)
i agree with @Leroy105 on the fact that the fets may be different, however i wonder if you are connecting the source to the load rather than to 0v, that would rise the source voltage hence the gate source voltage would be lower which in turn may reduce the output current, and according to the datasheets of both fets that should happen in a more apparent in the RFP30N06LE since it has a slightly higher vTh which means that the voltage at the load should be lower for the fet to activate and hence lower would be the current at the load