Have you tried to run the re-discovery task with the 'Run-as' option and use the account that you used for the initial discovery of the device? Do you still get the device configuration token error? But keep in mind, that the rediscovery task by itself won't update the big3d agent automatically on the F5 device. I would run to the rediscovery using a command prompt, and running the following command (from the folder where the F5 Management Pack is deployed, by default the %Program Files%\F5 Networks\Management Pack):
f5mpcmd /d:updatebig3d ip_address
where ip_address = the IP address of the F5 device
Julian