Thermostat crashes when mounted

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Hi all. After a firmware upgrade to 54.20, one of my thermostats is no longer functioning. I have new batteries and had no previous issues with this one, and it starts up with its usual hello, but now, as soon as it mounts it just crashes - turns itself off no mounting process and nothing on the display when turning it. Has anyone seen this? Any thoughts on how to fix?

Other info...
- I followed the ten second and one minute restart procedure but no help.

- I know that the firmware download was interrupted by a connection loss, and then a battery disconnect when I tried to resolve the connection prob. Corrupted firmware download maybe? Can I force another firmware load?