One that might be happening is now due to an overload with tech! Some of the mechs are now so used to tech telling them what to do that they never connect their brain!
One easy thing to cause misfire and never get found by highly trained techs is just simple bad plug wires.
They can come loose and as we drive fall on some engine part to short out and misfire. But when the techs doo the high value computer stuff, they fail to think about the wire only shorting as we drive, so the computer never shows the fault!
Real human eyes can find the burned spot but that requires engaging the brain and willingness to WORK the problem!
If they get the misfire when it is at their shop, have they connected it to a scope to show the misfire and does it show which plug? Or does it show it is a random misfire, putting the problem into other items that might cause random misfires?
OBD is a tool but it is meant to be a first stop, not the final answer!
I traded my last car because the computer kept telling them it was the battery, even though they agreed they had changed the battery twice already! It had a bug somewhere but three dealerships and many, many trips and they never found it, so we sold it to a dealer!