[Kos-Mos]

That's not the sear. Sear is the part under the MIDDLE prong.
That's the disconnector lever.

It should slide perfectly up/down.
If you put a bit or pressure on the hammer and it goes up, it can be the hammer pivot post that is cracked.
The post is used to hold both halfs of the rear frame assembly together (with a screw).
The can crack at the very base, making the hammer tweak to the right under the pressure of the spring and "lock" the disconnetor lever.

Try this:
Fire as normal.
When it "locks", take the slide and push it hard towards the frame/grip, with a slight twist to the right (clockwise). If you can hear a faint "tick", that's the disconnector snapping into place.

Look to bent/cracked hammer post or right-side midframe.
The plastic frames ALWAYS crack across the right-side grip hole and cause this.