Syma quadcopter not communicating with remote

I have a Symex X5C quadcopter. We've had it about a year and it's been great. However, in the last few times we went out with it, there's been trouble getting the drone to respond to the remote controller. My son has a knack of being able to twiddle the two joysticks and get it to respond, but it's been getting progressively more difficult. Our last trip out we had trouble with it, even with brand new batteries in the controller and drone, and at the end it went up and it wouldn't respond and wound up flying over a bunch of soccer players and landing on the roof of the playground bathrooms. We managed to get it down, but we haven't been able to get it to respond at all now.

Has anyone else had this kind of drone issue?