This is a good question, and it felt like nepotism. I do want to point out that this is all somewhat hazy memories from years ago when all of this happened, so take everything with a grain of salt (as usual). Also, a lot of this is going to sound like nepotism, which is most likely was, but this is hearsay from other people.
My understanding of how the "fixer" came into there position is a somewhat circuitous route. From my understanding (I didn't hear any of this directly from the "fixer" themselves, but other people who spent far more time with the "fixer" than myself), the "fixer" had spent about a decade out of the workforce prior to joining Tesla. My understanding is that they were raising kids while also dealing with aging parents. We'll just call this time the "fixer"'s work hiatus.
Prior to the hiatus, the "fixer" had moved into a small-team managerial role at a large, name-brand tech company during the late 90s/early 2000s. At the end of the hiatus, they leveraged some connections and somehow attained a director position at Tesla managing a team of about 30-40 people straight out of the hiatus.
From my understanding, the first team the "fixer" managed at Tesla didn't like working for them and after about 18 months, the team basically forced the "fixer" out. I'm not exactly sure what the team was doing to push the person out, but from what I heard, work basically ground to a halt for the entire team where they refused to work for the "fixer".
This was around the same time that the two projects went sideways that I mentioned, so the director I reported to was on the outs and the director's manager (a VP) was looking for someone who could step into the role. The VP somehow connected with the "fixer" and they worked out a deal where the "fixer" would lead the team on a 3-month probation period while the VP continued to look for someone to come into the position, while also giving the "fixer" a chance to earn the role.
(Side note: One other bit of context I want to provide is that the team I was on was about 50-60 or so people at this time right before the "fixer" came on. The "fixer" also did not have any sort of technical background and this team consisted of probably ~90% software professionals in some capacity. A lot of the conversations were very technical in nature, and the "fixer" did A LOT of delegating and "just tell me what decision you'd make and we'll do that" leadership.)
During this probation period, I thought the "fixer" actually did a good job getting a lay of the land, the social dynamics at play, and helped work out some inefficiencies. However, a lot of this improvement was done by bringing in consultants to do the deep dive, discover problems, and provide guidance to the "fixer" on how to address the problems.
Once the probation period was over, the consultants left and the "fixer" was in charge. Pretty quickly, the firings began and over the course of the next 5-6 months, more than 70% of the team under the "fixer" was replaced. At the same time, the team I was working for merged with another team, and the team size under the "fixer" shot up to about 100-120 people post-merge (I forget the exact number). The "fixer" also hired quite a few more people thinking more people get the same projects done faster.
To say the least, it was a pretty chaotic time because the entire team was under a lot of pressure with in-flight projects, not knowing if they were going to randomly be fired or not, new people to mentor/gel with, and lots of random projects being thrown at us.
About 6 months after I left, the "fixer" was fired and someone else who had extensive experience was brought in to right the ship. Per my understanding with people who were still working there about a year after the "fixer" left, the new person was very successful and had done a good job leading the team. Also, the person who I found to be my replacement stayed nearly 7 years at Tesla, so I guess I did a good job with that one.