I have been experiencing a lot of EMPTY_RESPONSE errors while using CometCachePro (also happens with the free version). After spending a couple days diving into this, I realized this was due to the Essential Grid plugin simply being active.
I wanted to make the plugin authors aware of this issue and also let other users be aware of the problems that Essential Grid will cause if used with CometCache. It's very sporadic and difficult to isolate but in the end, Essential Grid is the nemesis. Hopefully this will save a few people some headaches.