Cover Image with fixed background causes Problems in Chrome

[derweili]

Describe the bug
When using the cover image with a fixed background the image is not always shown correctly in chrome. Sometimes it is not visible and sometimes only a part is visible.

To Reproduce
Steps to reproduce the behavior:

1. Use Chrome 67, WP 4.9.8 and Gutenberg 3.7.0
2. Add a Cover Image Block to a post
3. Activate "Fixed Background"
4. The Image is not completely visible

This error exists both in the backend and in the frontend

This does not happen with all Images.

Expected behavior
The image should be completely visible

Screenshots

The image is only partly visible:

Here a Video for better understanding:

Desktop :

• OS: macOS 10.13.3
• Browser Chrome
• Version 67

Additional context
I think this bug has something to do with the bug described here:
https://stackoverflow.com/questions/20268962/fixed-attachment-background-image-flicker-disappear-in-chrome-when-coupled-with

The following CSS Code fixes this bug:
.wp-block-cover-image.has-parallax{ will-change: top; }

[karmatosed]

If we can get the same visual but with a browser fix, then yes let's get this done. Design wise it shouldn't change how looks.

[colorful-tones]

I've tested and reproduced the issue in Chrome 67 on macOS 10.13 in BrowserStack. I also tested Chrome 66, 68, and 69, Safari 11.1, Firefox 59, 60, 61, 62 with macOS 10.13. The bug is unique to Chrome 67 only.

I confirmed that will-change: top; does fix the issue in Chrome 67.

However, MDN Docs for will-change states the following:

The spec doesn't define the behavior of particular value, but it is common for transform to be a compositing layer hint. Chrome currently takes two actions, given particular CSS property idents: establish a new compositing layer or a new stacking context.

While using top for the will-change value works. It seems arbitrary. I recommend using transform, which is still arbitrary, but just a little less arbitrary :)

[jasmussen]

Given we're at Chrome 71 now, and I can't reproduce it, can we close this ticket?

Very sorry this did not receive a review sooner, it's been pretty hectic these past few months. For context, I recall trying to fix probably the same issue #2872 way back. I also remember this being fixed upstream, see discussion #2872 (comment).

[colorful-tones]

I just tested on Chrome 71.0.3578.98 macOS 10.14.3 WP 5.0.3 and I was no longer able to reproduce this.

[jasmussen]

Cool. Closing this for now, we can reopen if issues arise again.

[colorful-tones]

Further context... I did some more testing and verified this was not an issue. Please see: #11608 (comment)