I have recently experienced two short-lived problems with my 2nd Apex headlamp.
First, it went out while negotiating a tricky uphill crawl (the Hell Hole) in Mammoth Cave at Jenolan. It would not turn on again until I gave the battery box a hard slap. Ok after that.
Second, it went into a dim mode while coming oiut of the lower roof sniff in Elk River. Not out, but just about 1/3 intensity. It would still switch between modes! Again, a good clout to the battery box fixed it.
It would seem that these two problems were caused by poor contacts in the battery compartment, so they are different to the original problems of water ingress to the headpiece. The second incident WAS in water, and I did find later that water had extered the battery box. I have since ensured that the battery contacts are very clean (though I thought I was already doing that ….. !).
By the way, the previously described heatshrink tube fix for the battery box detachment issue, devised by Chalky and implemented on his and my units, has definitely eliminated that problem.