Let me revise the timeline I started this thread with to make it more accurate. Note: I am not claiming that the incidents listed below are all related. Some of them may be.
On Nov 18,2016 the Barstow Supercharger was rendered inoperative, reportedly due to the theft of multiple circuit breakers from the locked enclosure.
On Feb 23, 2017 the Cabazon Supercharger was rendered inoperative and took about 2 weeks to be put back into service. One TMC member reported that a Tesla owner they knew said that "the cables were cut", whatever that means. I haven't found a reliable first hand report of what actually happened.
On Mar 11, 2017 the Indio Supercharger was rendered inoperative. A TMC user reported "cables were stolen" fron the enclosure (not the charging cables attached to the pedestals) but it is not clear to me how they knew that. It is now back online.
On Mar 18, 2017, the Gustine, Bakersfield, and Buttonwillow Superchargers were all rendered inoperative on the same day. One TMC member,
@Ulmo , reported being at Gustine at 1257AM and posted, quote: "The SC was dark. A manufacturer Tesla Model S with a Tesla worker was there locking the equipment gate. I asked what was wrong and he said a circuit breaker failed, and a part went bad."
As of this post I don't have any information on what happened at Bakersfield and Buttonwillow, and my car nav shows they are now partially operational.
On Mar 20, 2017, the nav in my car shows Vacaville as "temporary closure". It's non-operational. No other information.
I find this many Superchargers going down in California over a relatively short time period suspicious. There are several possible explanations. I am not assuming that all these locations went down for the same reason.
In my opinion, the simplest explanation is theft of valuable parts, quite possibly by the same person(s). Another possible explanation is vandalism, possibly by the same person(s). Also possible is simple equipment failure (based on one report that may be what happened at Gustine) but I don't believe that is the explanation for most of the location problems.
I know of no information showing that any of those Supercharger locations were temporarily closed because Tesla was upgrading them in some manner. But it is possible.