The issue you're having appears to be tied to the software. It's possible that it's limited to the video file you're trying to play, such as when the file becomes corrupted. Another option is that the video link or file path is faulty or damaged, preventing you from loading the movie using the provided URL. It's also conceivable that the YouTube video you're attempting to watch has a file format that your iPhone OS doesn't support. MP4 is the preferred video file format for use with your iPhone.

1. If the issue is confined to your iPhone's YouTube app, shutting it will likely resolve the issue and give the app a new start when it relaunches. So here's what you'll need to do to make that happen:
2. On your iPhone, close the YouTube app. To do so, press and hold the Home button twice to open or launch the App Switcher.
3. Navigate and identify the app you're trying to close in the.App Switcher after it's launched. Swipe up the YouTube app preview off the screen to close it if you're using it. Do the same thing with any other apps you're using.
4. After dismissing the app, reset your iPhone and then relaunch it from the Apps screen as usual.