Timeout occurred while processing the operation - Nokia Flexi Content Optimizer

Summary: 
"Timeout occurred while processing the operation. "

We have a Nokia Flexi Content Optimizer (FCO) solution in our network and we have been struggling with this error for quite some time now. when the FCO is inline, some websites return this error, however the websites are accessible with no errors when the FCO is removed from the path.

Problem or Goal:

Some websites are not accessible with the cache inline, and return this error "Timeout occurred while processing the operation. "

Cause:

The FCO experts say the issues is that the cache sends a SYNC packet to the webserver but never receives a response, hence returning that error code to client's browser.

See screen shot below of the error code:

HTTP Error 504 Gateway timeout

Solution:

unfortunately, we are still struggling with this issue.

Here are a few pointers:
HTTP Error 504 Gateway timeout

Problem Solved?

Not Yet, will update once done, but leave a comment if you can help out. will be glad