To answer your questions in the video, I'm inclined to think your problem was loose t/c bolts all along. It's not necessarily that the bolts back out and the heads start hitting anything. It's the flexplate slopping back-n-forth rotationally with respect to the t/c because the bolt holes are larger than the bolt. In more severe cases you even see the holes starting to egg out from the banging and the threads on the bolt start to get mushed. Really loose, I can see the plate flexing and moving up/down the threads.
Plenty of other threads on
where the knocking was fixed by re-torquing the bolts.
I just rewatched the original video and it sounds like t/c bolts to me, including gong away under load or when reved. He even suggested it might be the t/c bolts. Can't say I've never overthought something myself.