Video controls missing in iOS 11.01

Hi.

I have a very strange problem in one of my app (not in all!):

All buttons are not visible.

I tested a lot and have no clues why this happens in one of my app.

Things I tried:

• Disabled my icon font
• Checked all CSS styles with Safari
• Changed status bar color and style

I still have no idea why this happens and couldn't find anything in Google.

But perhaps somebody has an idea which can help me?