edit: Never mind, I found your story about what happened to the Quark
https://www.candlepowerforums.com/posts/3336501#post3336501
I have had the same issues with my Quark Mini Titaniums, but one thing I found is that sometimes the problem is caused by an accumulation of debris in the threads.
In my case, the lights came with a BLACK oring and I find that over time, the black oring gets worn down, creating a gooey black substance that clogs the threads. The black goo appears to be made of chewed up oring and lube (I use the Deoxit that came with the lights).
Just last night, after using my Quark Mini Titanium for a couple hours on a wiring project, it was getting bad enough that it was skipping modes like crazy and I could hardly make it turn on without really tightening the head hard. Sure enough, after I opened it up, pulled off the oring and cleaned the threads with electronics cleaner, the light was working flawlessly.
One thing I am trying now is I took one of the clear orings from my Maratac AA, which seem to be tighter orings, and put that on in place of the black oring. I want to see if the clear oring holds up better to wear and doesn't produce black crud.
Just a disclaimer, I don't know for sure if the black crud in the threads is worn oring material, that is just a guess. I don't know what color the surface oxidization of titanium is, for example, maybe that's what it is? I don't know.