I just contacted AC support about this exact same issue last week. I have to restart AC, and most of the time it fortunately then resurrects the incomplete chart. However this only happens on my 2 laptops and not my desktop. They suggested that I remove all deleted items and unreconciled orders from 2013 and 2014. That did not help and I will be contacting them again on Monday. I would say it has only happening about the past 4 months or so although we upgraded to Windows 10 a year ago.
Very frustrating.

Theo A. Stephens, MD
Internal Medicine,
Baltimore, MD