Blank page usually happens when the result from the controller is malformed. To check, you can open a browser and type in the following and check the result:
where x.x.x.x is your controller’s IP address, /ja is a command that requests all json data as a whole, and a6d82bced638de3def1e9bbb4983225c is the md5hash of ‘opendoor’. As you said, after upgrade, the device key will reset back to opendoor, so this should work. The result should be a valid JSON string (you can use any online json parser to check if the result is valid or not, such as: http://json.parser.online.fr/
Perhaps you can perform a factory reset just to make sure all parameters are reset back to default values.