I've used Google Fi for years, and I've heard stories like these for years. Despite comments in this thread, I don't think these experiences are new; they're just more common now because more people are on Fi.
I think there are two major issues: first, Google doesn't really care all that much about Google Fi. It's just them keeping their foot in the water for later, not a major focus right now, so it doesn't get the attention and care it really needs. Second, Google Fi is honestly great, right up until the point it isn't: if you ask around the community, there's a strong split between people like me, who have had nothing but good experiences, and people like Jason, who have an amazingly awful experience. It's basically that Google Fi is thoroughly buggy: you're fine as long as you stay in the happy path, but the moment you get to something untested (stolen phone, FedEx loses shipment, the discount fiasco a couple weeks ago), everything goes to hell.
I've stuck with Fi so far because the pain I've hit has been negligible for me [1], but I currently assume that it's just a matter of time before I get burned in some capacity. It's a trade-off that makes sense, given how I use my phone, but it's annoying having that in the back of my mind.
[1]: The one thing they did flub was the Pixel 3 discount a couple weeks ago, wherein they accidentally charged and then refunded the entire value of a Pixel 3. Because I pay my bill by credit card, and because that card is nowhere near its credit limit, this was just two lines on a bill for me that I never really have to think about. But for those who pay their bill by debit, or who were near a limit, or whose bill rolled over between the charge and the refund, that was also a horrible experience that angered them about Fi. Those kinds of stories have been par for the course.