Boxster headlight problem

[Ace1]

I have a 2001 Boxster S that has developed a headlight issue and I could use some assistance from the collective wisdom of the forum.
It has aftermarket HID headlights that were in the car when I acquired it a little over a year ago, and seemed to work just fine until recently.
When the headlight switch is turned on, both headlights will illuminate, and then after about 10 - 30 seconds, the passenger side headlight will then go out. Originally thinking the bulb needed to be replaced, I had this done.
Within a week the issue returned. We swapped the ballast with the drivers side which has not experienced any issue, either before or after and works fine to this day. However the issue remained with the passenger side. At first when the problem returned, after the light would go out, turning the switch off and then back on, the light would come back on and stay on. Now this "fix" does not work, as the light will just go out again within 20 - 60 seconds or so.
We are stumped with what may be the cause. Could this be a loose connection somewhere or might this be a headlight switch problem ? .... Or something else ??? And if it is the switch, why does this only affect the passenger side and not both headlights ?
Appreciate in advance any suggestions or solutions !