Since 2016.12, opening Melodyne as a Region FX crashes Sonar or at least causes an audio drop out. When I render the Melodyne file, Sonar crashes or at least causes an audio drop out. I have participated in a recent thread about this.

As this was not happening until 2016.12, I am unfortunately considering rolling back to 2016.10. I avoided most of the issues reported in 2016.11, but Sonar was rock solid for me up to and including 2016.10.

If I roll back are there any issues? E.g., I presume plugins I have purchased recently will be picked up by the scan on start up as normal. Anything I need to be aware of? I really need didn't want to go down this road.

The only plugs that *may* revert will be Cake plugs. And, AFAIK, that would only be if a Cake plug was updated in the "rolled back to" version.
 

this may be a silly question but have you updated to Melodyne 4.1?
If not you may find this solves your problem

Hatstand
this may be a silly question but have you updated to Melodyne 4.1?
If not you may find this solves your problem

Yes, 4.1. 

In case it helps others, I resisted rolling back and by disabling all effects on the track I want to use Melodyne on, I've been able to use it multiple times today without a problem. Once done, I can switch the effects back on and all is well.