Video Player problems on iOS (Unity 2018)

We created a VR app that downloads/streams 360 stereo video from a server and displays it in the app for the viewer. All downloaded videos are 4096x2048 resolution H264 encoded MP4 files. The streaming videos are coming from Vimeo, and stream at 1080. This app is for Android as well as iOS.

We noticed that after downloading the videos to the iPhone (7, 8, XR) through the app, all we get is audio, but no video. We even down-res'd the videos to 2048x1024 and still, only audio. Also, we downloaded the videos outside the app, and they play just fine on the phones.

All videos are downloading, playing, and streaming just fine on the Android version of the app.

Does anyone know why iOS is failing to play the videos through the video player in Unity, but playing them just fine when downloaded outside of the app? Thanks for the help!