This looks very much to me like a problem many people have had with fixed backgrounds (of which parallax is one).
The webkit installation on your machine seems to get broken by certain plugins added to Chrome. The result is that anything you publish from that machine will do as you describe with fixed backgrounds.
I must stress that this problem occurs due to the installation on the machine from which the page is published but is manifested for all viewers… The same project file will work when published from another, unaffected machine.
Firstly, test if this is the case by publishing a simple page without parallax but containing a fixed background image using a stack such as Joes Jack or my Sections stack. Make sure that the fixed image is far enough down the page so that all of it is not within the viewport on page load.
Look at the resulting page in Chrome - does it suffer the same problem? If so, you will notice that any part of the image not in the viewport at load will not be displayed until you re-size the browser.
This happens because Chrome tries to save power by ignoring fixed image processing for areas that are not in the viewport. Clearly the problem above means that this is not working correctly.
If you verify that this is indeed the problem there are two possible solutions:
- Uninstall Chrome and all its plugins completely from your machine. Restart and re-install Chrome.
- This has worked for about 50% of people.
- Re-install OSX from the Apple combo update. (You will not loose any data - although obviously back up first anyway)
- This has worked for 100% of people where option 1 did not resolve the problem
Here is the link to the 10.11.3 combo update - you may of course need a different one depending on your current OSX version. https://support.apple.com/kb/DL1859?locale=en_US