It seems that once you click edit on one of the predefined device you can't save unless you first specify " text data for the device id attribute" (attached).
I am not sure how to do this as there is no such field
I've deleted all the relevant Devices (the one attached was the entry imported from the 8.301 backup file). I suspect that this was because of the endpoint function used on old firmware (7.x) )
At the moment I don't have any devices to test. Will let you know once I confirm