Has anyone reported slowness when there's a lot of 508 errors?
I had a situation last night where the load on the box was nothing, IO was nothing, the box was sleeping, but all web requests to the box took forever (15 seconds+) to load simple pages.
I saw there was someone getting a lot of traffic, which was all being throttled by CloudLinux, so you were spitting out a ton of 508 errors.
I ended up downgrading to 4.2.4, and the issue went away. (The user was still being throttled, but it didn't affect other customers).
I don't have time to troubleshoot the issue with you, but figured to let you know.