My guess is the bolt head is riding ABOVE the reciever track rather than in it. pull the bolt all the way back, apply pressure to the top of the bolt head until it overcomes a tiny spring on the side of the reciever rail and snaps into the track, push bolt forward while doing so.
The OBVIOUS indication of the bolt being not in the track is that you can lift the bolt head once it is past the charger bridge.
Of course, as stated above, the bolt head must be screwed all the way down. It won't go into the reciever in that condition but must be eased back a tiny bit.
A bit more, the bolt cocks on CLOSING so being uncocked when being inserted is normal. It is NOT a mouser!