If I rename a device in config.json the database gets inconsistent and I can not see former values of this device in the graph.
Rename device without loss of Database history
If you want to change the name and still see all data before, you must rename ist in the config.json and in the sqlite database as well. For this you can use the sqlitebrowser:
you have to change the name also in the table deviceAttribute in the column deviceID, after this you got your graph back