Well, resurrecting this from the dead..
Seems that I finally found the source of my issues.. I must have spent last year + troubleshooting this bugging problem. Unfortunately, it occurred so infrequently and whenever I tried something it went away to magically re-appear soon after I thought it was gone that I just lost hope.
Anyway, just sent my email to the support-AX860i@corsair.com hoping to get a decent resolution!
@Corsair Kevinhope you can assist to speed things up if possible, can provide the ticket id.
Ps. Interestingly enough, looking at potential reasons in my case, I don't believe use of too long screws is at all likely, as I have a Obsidian 650D which has a neat mounting bracket so I never used PSU screws at the back of the case as it was mounted so well and secure. Certainly threads look like new!