My Finished Export has Glitches

I have recently been editing videos that were filmed on my a couple of iPhones. I've edited the content down to about 30 mins or so. Everything looks fine and plays fine in the Primiere Rush Editor but when I export it, no matter the settings of the export, the final rendered video flashes and twitches gray screens for about the first minute and a half. It seems to get better after that, but still randomly has it happen throughout the video. It's very frustrating. It's my first time editing with this and to be honest, it hasn't been the been experience since I'm having so much trouble just exporting the video. 

I'm on iOS. Macbook Pro. 

Can anyone help?