Stuttering video

Hi

I filmed on my Iphone 8 plus using the Adobe Rush app. I've uploaded the files to my desktop and imported into Rush. When I play the files, without any editing, the video is stuttering. I'm assuming it's something to do with frame rate but I don't understand what that means, or how to make it play smoothly. When I export, it plays the same stuttering effect.

Playback on my phone and from desktop in Quicktime Player is fine.

Any ideas?