At first I wasnt certain if it was melodyne - so I tried the vocal sync tool and also the drum replacer - in the same project.  All three effects - after inserted - show a blank waveform.   In this same project - I was working earlier and employing the drum replacer tool and it is still functioning?
 
Anyone ever encounter this?
Very confused

Hi. I remember having this issue with Melodyne. But it was due to it not being activated, when upgrading pc to Win 10. Worked after activating it. Could that be the case for you?
Best of luck.