Graph remains grey and shows no curves at all.
Possible Causes & Resolutions:
Avoid very fast switching between pages. This causes overloading of the browser.
Close alle open browser connection (HMI app) and wait for >2 min.
Now you should be able to open the HMI without error message.
Close HMI app on iPads with home button:
Close HMI app on newer iPads without home button: