I have followed your sorry tale from the start and you have my sympathies.
Is this effect/problem also an audible effect or visible as witness marks on the bore?
I must admit to not having heard this term before, and have spent much of my hobby life inside engines of one sort or another (not my profession) but have no experience of aircraft power units apart from reassembling a C65 and a C90.
The rings should be a good running fit in the grooves so I cannot see how any chatter can occur especially at the RPM that this will operate. I fail to see how any effect can be caused by the ends of the ring assuming that it is 'gapped' correctly, and I think modern automotive and small engine rings are supplied to size these days although I always check square in the lower part of the bore.
Strange!