Sorry to hear the update has been a problem for you guys. The problem is that I can't reproduce the problem! Everything seems to be working normally for me.
First of all, please confirm that you are using the latest version 1.2.1.
What you can do is open developer tools in chrome, (or some other browser with developer tools), go to the console, and observe what comes up (if anything) there when you try to load a less file - both before and after. Chances are, you will see an error there. If so, please share what you see.
Does it only happen for LESS files? what about CSS files?
It's worth mentioning that if you are using the pagelines debug function 'plprint( $some_data )' somewhere in your site, this will throw a wrench in things when its being output to the footer and break the data that is being returned via ajax. This will cause the file load (or any other ajax function like complie/save) to fail and causing the loader to show spinning endlessly, and nothing else to work. There's no reason though however that this would change with the most recent version of LESS Developer.
Please see what comes up in the developer tools console and let me know!