Lycoming piston pin plug failures have been around for a long time. In the late 80's through mid 90's, I worked closely with an engine overhaul shop, and investigated a number of these. Though I know longer retain any specific details, the overlying theme is that the original Lycoming parts are comprised of the tubular shaped wrist pin, and the two aluminum plugs which will slid in the ends of the pin. There was an aftermarket wrist pin which had a solid aliminum pin rveted within the steel wrist pin. It worked well.
The aluminum plugs keep the steel wrist pin centered within the cylinder diameter, without damaging the cylinder walls (it's softer). Unfortunately, the original design is lacking, in that the pin wobbles a little up and down with each stroke. The wobbling gets worse and worse, 'till the pin is able to roll over in it's cavity in the piston. When it starts to roll over, nothing stops it, and it can turn whicever way it wants. In variably, it beats it's way out through the piston skirt, and is now floating around in the crankcase. True to Murphy's law, it will go where it can do the most damage, and will find it's way between the case casting, and the head of a valve lifter. When the camshaft closes the lifter, the chunk of plug jams everything, and jams the lifter open (= valve closed). this will really damage the camshaft, and usually break off a part of the head of the lifter, which now bounds around the case itself.
Added to the trauma, is that the high cam in Lycomings (as opposed to the low cam of Continentals, which benefits from the drip oil off the crackshaft) are not quiet as well lubricated, so are even more quickly damaged (not that oil would really have stopped it anyway).
I do have some photos of a few engines we documented, I'll dig them out, and post them. I do not recall any particular set of conditions which caused this condition, it seemd varied across different circumstances. It would take a few hundred hours of running time to happen though.
Your only real means of detection is oil analysis, and noticing way too much aluminum in the oil (knowing that a little is normal). Other than that, you're pulling cylinders to find the condition. The solid wrist pins were the solution. I have not been associated with this problem for many years now, and am not up on the latest developments. I hope that the market forces have made the more durable wrist pins. This is not a condition to be taken lightly. If you think it' happening, get the parts replaced quickly, it will be very costly, and you'll be gliding, if the full damage occurs....