From what you've written, I'm assuming the hammer is dropping, however the round doesn't discharge and there's no sign of firing pin strike on the primer. If this is accurate, I would look at firing pin spring and main spring before troubleshooting a failure to return to battery.
If it's not fully in battery and the hammer drops, you've got some serious issues.
My initial thought is that the FP spring is very light or perhaps someone lightened the main spring. Both are pretty easy to check and cheap to replace with factory springs. Once you do that and if you're still get 'no strikes' (as opposed to light strikes) you'll need to look more into slide timing and trigger mechanics.