car is cranking but not starting, wait about an hour, able to start?

The first time the car's not starting, the security light's on when the car's off. Thank for info on website, I was able to deactivate it and started the car (getting no help from Mazda). Two months later, it's happened again, this time no light on, no code. After the car's starting again, I brought it to local shop to replace battery (even the battery is still ok, but old ~5years old, so it's time to change), check the alternator (good), doing the fuel system service with fuel injector cleaning, air filter change as well as oil/oil filter change ... (please note, the mechanic guy could not recreate the issue). Then last week (three weeks later), it was happened again, I guess it might be some sensor. I know it's no use to bring it to the shop for the intermitted failure; especially if it is not recreated. I guess I have to wait for a while to see. In the meantime, I would like to educate myself so that I can communicate and understand the work from the shop later.

Did the mechanic have the same key you were using when you had the problem or was it the spare key? I had that happen last year with a Toyota Highlander. Her spare key was never used and new while here key was used daily and was the problem. Once we had a new key made the problem was solved. Good luck.

We (I and mechanic used the same key) as I only have one key now (lost the other one. Maybe I should try to have new key made. Thanks.