All depends on what device you testing on. A few steps that could help you to find the issue:
- Inspect your app in Safari to see the console logs, that could tell you if there is a runtime error. You can check your xcode logs too
- If you don't see any console error or you get something that is not interpretable eg.:SyntaxError: Unexpected token '{'. Possible that your web app bundle is not supporting older webkit engine. You need to rebuild your web app with a different target so that it can run on older browser.