Background no longer fixed in Aviator

Site URL: https://www.lauranoxon.com

Hi!

This has been driving me crazy -- in the Aviator template, my background has always been fixed while the content on top of it scrolls. However, I noticed recently that on some pages the background stretched to cover the entire height of the page, and those backgrounds no longer stay fixed. I changed them to "contain" so at least it doesn't look warped, but despite having "Fix position" as "fixed" on all pages, it clearly is not.

Can anyone advise? 

Thanks!

Update: it looks fine in Safari! The stretching background and non-fixed issue appears in Chrome. I have not tried other browsers