I realize that these forums are just for the Sydney theme and NOT for related plugins, but there’s an issue with a couple of the most widely used ones that you might like to address.
First off like many others, I use Autoptimize for minification.
Then I use Foo-Gallery for the lightbox slideshow (this effect may well happen with ANY lightbox), and finally, it appears ANY ‘follow-me-on-social-networks-widget’ also has the undesired effect.
On any other website using any theme, the above three combinations run without problems.
Normally I wouldn’t bother and move onto a theme that DOES work with the above combo - but this theme has something special about it and is worth persevering with.
Any help and guidance would be most welcome!