In 2017, basically all the Google Fiber software teams went on hiatus (mine included). I can't speak to the timing or rationale but my theory is that the Google leadership couldn't decide if the future of Internet was wired or wireless and a huge investment in wired may be invalidated if the future Internet was wired so rather than guessing wrong, the leadership simply decided to definitely lose by mothballing the whole thing.
At that time, several proposed cities were put on hiatus, some of which had already hired local people. In 2019, Google Fiber exited Louisville, KY, paying penalties for doing so [1]. That really seemed like the end.
I also speculated that Google had tried or was trying to sell the whole thing. I do wonder if the resurrection it seems to have undergone is simply a result of the inability to find a buyer. I have no information to suggest that one way or the other.
There were missteps along the way. A big example was the TV software that was originally an acquisition, SageTV [2]. Somebody decided it would be a good idea to completely rewrite this Java app into Web technologies on an embedded Chrome instance on a memory-limited embedded CPU in a set-top box. Originally planned to take 6 months, it took (IIRC) 3.5+ years.
But that didn't actually matter at all in the grand scheme of things because the biggest problem and the biggest cost was physical network infrastructure. It is incredibly expensive and most of the issues are hyperlocal (eg soil conditions, city ordinances) as well as decades of lobbying by ISPs of state and local governments to create barriers against competition.
[1]: https://arstechnica.com/information-technology/2019/04/googl...
[2]: https://arstechnica.com/information-technology/2011/06/googl...