Found a fix for my Google Nest (3rd gen).
I moved the Nest (it's on a stand) to the same room as its Heat Link under the boiler. Next day or so, the Usage history started to transfer from the Nest to the Android app (screenshot below). HOORAY!!!
(Earlier tried changing the Nest's network connection to a different WiFi point's 5GHz band, but this didn't work)
My history just started showing up again for no apparent reason about a week aga, after not showing up for 5 or 6 months. Coincidentally (maybe) this happened shortly after I had to speak to a Next representative for help getting it to join my wi-fi network after a power outage. At that time I told her how angry people in the Nest community were about this problem and that it seems Google has not responded. She said, "Yeah, we're having a problem with that." To which I said that would have been nice (for all of us to hear) when we first reported the problem instead of crickets. About a week later my history was working again. Hmmmm.....