It sounds like you’ve already gone through many of the things that usually resolve these issues: verify the checksum, re-flash it, and try a different SD card. And even went beyond that and tried the mirror and another Raspberry Pi image, too.
I agree it seems like your hardware is fine and it’s an issue with the image/flashing ptocess, but I use the hestia-pi-ONE-v1.4-dev-bullseye-6185.img.xz with every unit I build, so this one is quite the puzzler.
When you say it “kept restarting with the original boot sequence”, that was before you flashed it, correct?
And do you mean that it would boot up and ask you to connect to the HESTIAPI access point, and then switch into the thetmostat UI after about 500 seconds? So it’d work only in offline mode.
After flashing the card, when “the image kept failing” does this mean it failed to boot at all, or that it went through the new thermostat setup and then only worked as an offline thermostat?
I use dd in Linux to flash my cards. If you can tell me what opeating system you are using Etcher on, I can download that software and try to reproduce the issue. Also, if you can let me know if you are using a Raspberry Pi Zero W or Zero 2 W, that will help me make sure I’m doing things exactly the same as you.
I also noticed that the installation page mentions Windows not being reliable at flashing images, but I do have one Windows machine that I can use to see of that’s the case if you’re using Windows.
I think we should be able to get to the bottom of this.