Hi,
Thank you for the details!
Looking at the page I see some of the plugin styling completely missing. My guess is, that the cache plugin (or optimizer) you may be using did not pick up the file, or it’s cache is not cleared.
– Try clearing the minfy/optimizer cache to see if that refreshes the files
– Try turning it off temporarily (especially the minify/combine feature)
You can also try to switch the CSS loading method to inline, that will very likely help. I see you may be using SG Optimizer, unfortunately that one has bugs (maybe they are fixed now) with CSS combine feature, where some files are not parsed even though they are queued for minification. That would perfectly explain the issue.