Hi guys,
just want to share my experience regarding this... Since I was going crazy.
As mentioned by Scott, one of the reason why this "error" occurs is when there's a class that is not compiling. Fun enough seems that Setup -> Apex Class -> Compile All classes is not a reliable tool to check if you have a broken reference in your code :\
One of my trigger was referencing a method that did not exist anymore but when trying to "Compile all classes" I was getting the message: "All classes compiled successful"... Really disturbing.
Enabling IlluminatedCloud log I was able to identify this issue, remove the broken reference in the trigger and now everything works fine.
In the meantime I opened a Case to SF support to explain me why the hell that happen ;)
Cheers,
Marco