Speed (MPH) reading in Video and analysis is about half of actual MPH during replay

I just used the Track Addict for the first time and my MPH reading is about half of actual MPH on video and lap analysis. This occurred with the previous track app I was using and was hoping the change to Track Addict would correct this issue. I am using an iPhone 7 mounted to the front windshield on a '16 Camaro SS, ios 12.2, and a Kiwi 3 OBDII reader.

During the video replay the MPH is the same using either function: OBD or non-OBD. A friend downloaded the app for the same weekend and her MPH is reading perfect with no OBDII reader and an iPhone 7.

Please let me know what I can do to help resolve this issue. Thanks!

Just following up from the original post to learn if anyone else has had the speed read incorrectly and the solution without going to an external GPS?