How much data have you got in your EmonCMS? Is it less than one full day?
Where did you see that error, was it in the Browsers debug console (F12) or was it a pop-up message?
[EDIT], this post has a method to delete the app and try again.
Well the problem was related to if there are not a full data of data this will produce this error. There error will show as a pop-up message. Let me review the code if I’m able to provide a fix to this case.
[Fixed Typo]