I thought my belt had gone a couple weeks ago. Halfway through the mower was struggling up the hill and lacked power. I smiled and thought 'belt's 4 years old, with this hill it's probably shot'. I pulled the spark plug boot before tipping it on its side and lo and behold, the spark plug was barely making contact with the wire. Something must have dislodged it during the mow.
Went ahead with the replacement. The existing belt was in pretty good shape, didn't see the wear indicating it was bad. I feel like the pace is better with the new belt so the old was most likely a bit stretched.
Point being, I was dead set on it being a belt issue and discovered the spark plug connection