Went out shooting with the older daughter yesterday and had 3 light strikes with no boom. I've seen this from my Ruger Mk 1 but not from the Glock so I'm guessing it's the same problem. In the Ruger, the hammer spring is hidden in the widget that disassembles the gun. You never think to check it and it doesn't lend itself to disassembly, but if you don't clean it at least by running some solvent through it, your Ruger gets finicky about what ammo it's going to use.
The Glock is striker fired but the issue of a spring in a confined and probably dirty area is certainly there. NOTE TO SELF: In case you forgot, when parts are retained by a cover that comes off by sliding, there's probably a spring or two under the cover with enough stored energy to place it in low orbit. If you have never taken the cover off, the correct location and orientation of the errant parts will NOT be readily apparent. Which is why they made the internet.