This is a common problem with all the focal headphones but mostly the elex because it uses a thinner voice coil wire than the clear.
Even the utopia is not immune to this problem.
A little background on what I did. I wanted to upgrade the driver wire in the clear to mundorf silver/gold 18awg to see how much an improvement it would yield in sound quality. The simple answer is, it yielded a very significant improvement. The problem is that it seems to have accelerated the voice coil wire solder joint failure, left driver died a day after I swapped the wire. At this point I was not aware of the driver failure as a known problem. Luckily for me the joint just lost continuity and the wire was still intact. So I carefully removed the silicon insulation and desoldered the joint and resoldered using mundorf supreme solder.
This brought the driver back to life but it was clipping. I opened it up to examine the joint again, in the tiny blue circle you can see I was a bit sloppy with my soldering. Its a delicate joint and I had trouble soldering it due to the size of the wire and my shaky hands. I adjusted it so that the joint held as much wire as possible without the tip sticking out like in the pic. This fixed the clipping issue.
Secondary problem, the left driver with the mundorf solder sounded alot better than the right side with the stock solder. I really did not want to do the other side as it was nerve racking to resolder it. But after a week, I couldn't ignore it any more, the channel imbalance was too great, so I ended up resoldering the right side as well.
This is how I know that the solder that focal uses on the voice coil wire is trash. I speculated whether it was the silicon insulation that was the issue but its definitely the solder. I don't know what kind of solder it is but it is not good, pretty much all of the solder they use on the clear and elex is just crap.
Since I'm pretty decent at soldering, it wasn't too much of a problem for me, I can do this very easily now but for others that dont know how to solder, it will be a problem. Its a fairly easy fix as long as the wire doesn't pop, sound quality improvement was definitely worth it though. I now have about 3 months daily driving the headphones after doing this with no issues with my clear.