Hello,
I am also experiencing these problems of CSS not working right with the Avada 3.8 update. I know is not your job to make it compatible with every theme out there but I was wondering if anyone figured out a fix for it.
It works alright with CSS disabled and only JS enabled, but obviously the idea is to have it all working.
I believe in Avada 3.8 they are trying to minimize the code also with LESS CSS but that is an advanced feature in the theme and is disabled by default.
The theme has a W3TC comment at the footer for hooks purposes I believe.
Some of my sites are stuck in 3.7 until I can figure out a way to make it work, because Autoptimize is too awesome to ditch it for an update.
I have a site for testing purposes with the problem.
Frank, let me know if you would like to access the backend if you would like to take a look at it with the new version.