The Sig 320 pistol was a really bad mechanical design.
There have been a number of revisions to the pistol over the years, and when UD's have occured Sig has paid a metric ass ton to keep most of them out of the courts.
I'll be honest I don't like Ron Cohen, their CEO, he took a company that was renown for their firearms and has scrimped on pretty much anything trying to save a penny on the manufacture.
Sig however has a voluntary upgrade program at no cost.
The P320® Voluntary Upgrade Program is a SIG SAUER initiative to upgrade P320 pistols at no additional cost.
www.sigsauer.com
One can google Sig P320 Sear Mechanism and find a lot of various versions and YouTube videos about the issues.
Sig has been so kind to send a process serve to my house in the night to serve me in the past when I was an expert witness for another case - so I will refrain from dragging them further through the mud, and let folks look for themselves.