Howdy. I bought a Phantom 3 Pro when it first came out. But I haven't used it for a year or more. This past weekend I charged up the batteries and controller, updated the Firmware, and took it for a spin.

But the frame rate, which used to be buttery smooth, is now super slow. Like one frame every second or two slow. Even being right next to it. And sometimes it only redraws half the screen every second or two. Makes it completely unusable.

I'm using an iPad Air (the same one I used previously when it worked great). I closed all other apps except for the DJI app.

Any suggestions on how to fix?

Being right next to it is wrong.  You need some separation.  It's like if I shouted into your ear, you'd hear me but you wouldn't understand me.  

My suggestion is to reinstall the Go app.  

But wait and see what some others say.  

Good luck