Fixed div overlays absolute with higher z-index only in one device. WHY

I have the next code

<div id='main' style='position:absolute'>
<div id='container' style='position:relative;z-index:1'>
<div id='bgd' style='position:fixed; z-index:1'>
</div>
</div>
<div id='content' style='position:absolute; z-index:15;'>
</div>
</div>

What do I get?

• iOS 13 - content over bgd

• Desktop Opera 65 - content over bgd

• Android 5 WebView 67 - the same

• Android 4 WebView 75(or something about this) - the same

• Android 7 WebView 77 - the same

• IE 11 - the same

Now I bought a new phone for testing, it runs under Android 8.1, chrome is 69.

• So new phone - content behind bgd.

Please, tell me what to do. I tried a lot of things