I’ve seen multiple security videos of P320’s going off in holsters in the field with no plausible way anyone or anything could have pulled the trigger.
The range video where they are standing on the line was allegedly a modified gun with non-Sig upper and trigger.
Officer standing and moves slightly and it goes off, with their hands in front of them? (Eyewitness)
And at least 3 others. There are some good compilation videos out there.
A gun in a holster can fire when it is moved and the holster is poorly fit, incorrectly configured, or there anything caught in it like tail of a shirt, drawstring. Also, many police have a flashlight on their pistol, which opens up space quite a bit making it easier for things to get caught inside.