Hi to
Perthmower and
Grumpy,I had this problem when I had the Briggs and Stratton fitted, one of the screws fell out on the lawn when I was mowing. I consequently ran over it and took a nick out of one of the cylinder blades and ruined my bedknife.

With re-grinds, the reel in back to normal, and I had a new bedknife ground and fitted just after the incident.
An expensive exercise!