Judging by the tactical silence around the TRVZB firmware update, it looks like the dev team got absolutely steamrolled by the issue. And it doesn’t seem to be just the download or installation part — something else clearly refused to cooperate 
Looks like bailing out from the TRVZB ecosystem into Home Assistant was the right call after all — the thing has been running smoothly for days now with schedule automations, mode switching, and external sensors. Quite a contrast to the rather… underwhelming cooperation with the NSPP, where the thermostats kept periodically breaking up and getting back together like a dysfunctional couple.
Sonoff even cooked up a so‑called quirk for TRVZB in ZHA. It’s oddly structured, the code is half‑baked and a bit twisted, but hey — it works. When I get some time, I’ll dig into it and maybe polish a few things.
Addendum
Well, it no longer works. After updating HA to 2026.2.0, many entities stopped being available. It turned out that the working quirk is now built into ZHA, and simply removing the Sonoff‑made one was enough to regain control. Let’s say it’s not full control, because you still have to account for the peculiarities of the TRVZB firmware.
For example, there is absolutely no way to convince the TRVZB to cooperate with an external temperature sensor. But there is a workaround. The Better Thermostat integration handles this elegantly by taking over the control logic and bypassing the buggy TRVZB firmware. It treats the TRVZB as a not‑so‑smart device. And because it offers extensive configuration that doesn’t get into deep conflicts with the device’s twisted firmware logic, even features equivalent to Adaptive Mode work correctly — and in several flavors. Also with firmware 1.4.4, which finally downloaded onto all of my TRVZBs.
Finally, everything behaves according to common sense and expectations in ZHA. If anyone is tired of wrestling with the TRVZB in eWeLink, I highly recommend going in this direction.