Something In my #5 Cylinder?

I can't imagine at that CR the piston is anywhere near the plug. For that to happen, something went wrong.

Most likely, something came off of the PC or the carb or maybe your intake system can pick up a rock or something and it found its way into the engine and found a home in the number 5 cylinder.

It's gone now, so you may never know what it was. But most likely, you have hurt that Rod bearing enough that as the RPM,s go up, the piston can come up and smack the ground wire.

You could index the plug...but you ain't fixing the issue.

You can hurt a bearing enough to close up the gap on a plug and not make noise. BTDT many times.

Your engine is telling you something. Get a handle on it before it eats your wallet.