Wonder, is the storage area for your mower damp by chance? Sounds like there may be moisture in the coil area preventing good spark. Otherwise, does it seem to be a fuel issue, or an ignition problem, or can you tell at this time?
Well, a procedure that works for many is to "bake" the coil. You take it off the machine, set it on a piece of foil, and put it in the oven at 200 degrees for about an hour. That will remove any moisture inside the unit. Sometimes it works for one or 2 mows, sometimes it is a permanent fix. Worth a try, none-the-less. I recently replaced the coil on my 10525. It was about $50 at the mower shop.