That happened to my 1G P-3AT initially. I figured it was a likely due to a new/stiff magazine spring. I worked the follower up & down with a ruler a couiple of dozen times and it did not repeat.
How many times have you fully loaded the mag? If not much, perhaps it is still a bit stiff. Maybe also disassemble the mag to make sure all is OK in there.
How many times have you fully loaded the mag? If not much, perhaps it is still a bit stiff. Maybe also disassemble the mag to make sure all is OK in there.