I've been asked:
 

Somebody with a Luger asked :
If he manually loads the weapon, (pulls the toggle) and then pulls the trigger, his gun fires and reloads the next round in the chamber. If he pulls the trigger again, the gun will not fire.
If he reloads again manually by pulling the toggle, then the gun fires but the next round will not fire again.
What could cause his problem?

I 've thought maybe somebody here has a clue. I thought it could be the trigger, but I have not seen this gun.
I don't know what kind of luger it is.

Sounds like the firing pin not resetting after the shot.

Sear / firing pin contact should be checked.

or a sticky disconnector

--Dwight

More likely the FP is cocking, but the disconnector is not pushing under the trigger lever in the side plate. TH

Thank you all for your kind advise!

I'll let him know.

Hugh has a fix for this. Look for a sticky. under repairs, restorations. "Cocking Problem'. This worked for my alphabet 30 cal.

FN

Thanks, Norm!