I think weight positioned outboard at the stern (= lever-arm advantage), as in a heavy dingy&motor on davits, plus wind generator, plus radar, plus solar panels, plus whatever else, are potentially culprits. I don't know if you have any of those items, but an anchor locker holding ground tackle is a feature (expectation) designed into the boat, whereas those stern-mounted items mentioned likely are not being add-on, etc. When hitting a wave, all that outboard weight at the stern might allow the bow to "rock up" farther than it normally would as the wave passes under. That sets the whole thing in motion, and keeps it going w/ additional wave hits. I once hobbyhorsed > 70 n.mi. motorsailing across the eastern GOM in an IP-37 with chain up front, but also a fully enclosed cockpit plus dinghy w/ motor hanging on stern davits & a wind generator mounted on the stern. It was slow and miserable.