pressure plate experts

IMO
the cover is flexing or the marcel is too stiff.
EDIT
I mean mechanically speaking those are your only two options, right?

Well there is a third one but you already said the disc was correctly installed.
Which would be with the flat side toward the flywheel........... irregardless of how it may be marked......

And if the disc was in backwards, that would certainly cause the disc to behave like a Bellville Washer and "pop"
as would flywheel bolts with heads that are up too high...... The heads have to be below the machined surface, and no loc-washers here; the oem bolts are special low-profile.