If you have a set of calipers, measure from the trigger pin hole to the trigger housing pin hole on the frame that doesn't fire and compare it to the frame that did work. If the non working frame is shorter, the cruciform will come off the sear early causing light primer strikes.
If you have less than two thirds engagement as shown in a previous post, you need to bend the trailing section up a hair until you have enough engagement. This won't fix a short frame problem though it might work for a little while you will run into a dead trigger (you get to the end of the trigger pull and it doesn't release the sear.)
As far as how to fix the engagement by bending the cruciform, I am not a Glock armorer with all the specialized tools so I use a small vice, a large punch, and a small hammer. Make a small, barely measurable adjustment, reassemble and test. Might take me a few tries, so a few assemble and disassemble cycles are expected.
If someone else has a better method, please chime in as I am always willing to learn something new myself .