Let me start off by saying I'm not an "engine guy", nor did I stay at the Holiday Inn Express, but I was just reading the Kitplanes article about vernatherms. That sliver of metal looks a lot like what might come off of where the beveled end of the vernatherm seats against the stop. The article even shows one with a worn end, and I was wondering if after some time a sliver of the beveled end came off.
Probably not the case that this is your problem, but if you can't find anything else it may worth a look? And it looks like it might be fairly easy to check.
If you get Kitplanes, the picture I'm referring to is on page 24 of the August 2021 edition.