I have this issue with a number of my websites since migrating from various cache plug-ins to Hummingbird.
It seems that the pages do not render properly when minified and was hoping someone else had this problem and was able to rectify it.
This issue does not happen all the time though, but it happens some websites weekly while others monthly.
One interesting point to note is that the Gzip compression is not working for html, works fine for css and js though. Might it be related?
Thank you for your help,