Engine won't start

I have a 2017 Murray with a Briggs and Stratton 625 EX engine. I hadn't any issues with this mower until this week.

The engine started up no problems. I mowed the perimeter of the yard and turned off the engine to move chairs out of the way and the mower wouldn't start. I mower had the original spark. I changed the plug and it still wouldn't start. I changed the oil the 2nd time this season and it started up. I mowed the back lawn and shut it off several times and it started up easyily. Yet today it won't start again. Thanks for any ideas.