Bent valves are likely. Even though the camshaft wasn't turning when keyway came out, some valves were suspended in position that pistons could hit as they continued (incorrect timing). Very shortly contact occurred. Higher engine speed just masks the missing, it's probably there. This was exactly the scenario that happened to me w/ Acura 2.5TL.

Time to pull the cylinder head or have an internal examination w/ borescope for piston damage.

good luck