So I tried to change the firmware on a device by going to Product -> Devices -> View Device -> Edit. I chose the new firmware version, made sure “Flash now” was checked, and clicked Done. I opened Chrome’s dev tools after trying this a few times, and nothing was ever posted to the server. However, I tried it one more time, this time changing an arbitrary field (Notes), and the changes did post. So, I’m guessing your form validation isn’t correct. You might want to check it out.
BUG with device edit screen in console - Can't flash a device in my product to a new firmware version