I was about to say it was a bad starter solenoid or bad starter in general. Glad it still runs. I was about to think it was a bad fuel system. Dirty carb or fuel solenoid. Like you said also a bad coil.
Don't feel bad about not noticing the blades were engaged. I'd like to have a dollar for every time I've forgotten to connect the spark plug on the push mowers I've worked on!!
When I pulled it out from under the shelter. I didn't see that the blades were engaged until I realized that something didn't looked right around the keyswitch.
