Sig Sauer P365 trigger does nothing, except when gun is shaken hard

Well, I might have screwed up a perfectly good P365! I have two of them and disassembled and reassembled them. One works fine now, but the other one... When I pull the trigger during dry fire, there is spring tension on the trigger, and it goes all the way back, but nothing else happens. Sometimes, if I then shake the pistol really hard (while the trigger is held back all the way), there's a noise that I presume is the striker releasing, and then the slide needs to be re-racked to reset the trigger, as would be normal after dry-firing.

To my eye, there is nothing different between the FCU of the working gun and the non-working one. When I push down on the sear, it moves, and there is spring tension pushing it back up. The sear pin looks to be pushed in all the way.

The only thing I notice that looks a bit odd is that the striker has a little bit of forward and backward play in the striker channel, whereas the one in my working gun doesn't move, but I don't know if that's normal.

Any help would be GREATLY appreciated. Thank you, wise armorers!

Here is a video of the play in the striker assembly: https://i.imgur.com/YHK0cqp.mp4. I wasn't able to put the full-quality FCU photos in the post because they came out huge, but higher-quality zoomable photos can be found here: https://imgur.com/a/7hqFPCb Below are smaller-size versions of the same FCU photos.

https://i.imgur.com/7qwCKed.png

Your striker movement is similar to my 365 in .380.

I suspect your sear pin is not fully seated or you have a damaged sear spring. If you disassembled the FCU completely, I’d start over ensuring that the sear pin is fully seated.

In armorer school, I had one I reassembled without a fully seated sear spring and everything looked good until I tried to dry fire/function test.

Regards.