XF 1.5 504 No Response from Server Error (reported without direct action)

[Live Free]

Some users have reported a semi-frequent, consistent server error that appears to occur randomly to the user. It’s frequent enough (apparently) that a large number of users are experiencing it. The user reporting the error said it’s experienced randomly when viewing parts of the forum, but not on specific actions.

The member reported “I wasn't actually doing anything, it just popped up, not in response to a click or anything” and that he can simply exit the error and continue using the site.

The user claimed it happens more frequently in IE than in Chrome or Firefox. The same user reported in four times within an power, all while viewing the same thread.

The error is a “No Response from Server” error, HTTP status code 504.

Looking at the XF admin server log, I do have a frequent error related to a custom add-on, but it doesn’t appear to be related. I'm looking into this concurrently, and will of course consider it the most likely candidate if I can't dig up anything else. Unfortunately I can't test it since the error seems to appear randomly.

How should I proceed from here? What are common causes of a 504 error?

Are there any other server-sided logs I should look for information in?

 

[Optic]

Your screenshot indicates the request is being filtered through a proxy/security package called Clearswift - it’s not clear if this is from your web host or the network connection your users are visiting from (corporate or work ?)

 

[Live Free]

Your screenshot indicates the request is being filtered through a proxy/security package called Clearswift - it’s not clear if this is from your web host or the network connection your users are visiting from (corporate or work ?)

I’m not familiar with ClearSwift but it appears to me a browser extension the end user is using. I suppose confirming the problem exists outside ClearSwift is somewhere to start but I’m still at a huge loss here.