I'm just using Vvocal installed from from other installed Xn versions for now cause I'm too busy.

I wonder how many of you having problems are using a different sample rate, or possibly a something different than 44.1 kHz ?
Possibly Melodyne is having problems interrupting the different/higher quality audio, like 48, 96, exc.
Which in theory it shouldn't but I wonder if that's what might also cause some problems.
 
I run almost exclusively, always 24 bit / 44.1 kHz and haven't had a crash with any region FX in over a year and I use each one (Drum replacer, Vocal synch and Melodyne on every single project.)

Been experiencing the same issue.
After many tests, I believe the problem is I the "blob monitoring" function.
Monitoring appears to gave been damaged on my setup since they updated.
I have found that, if I can launch a region FX of melodyne, and go into options and turn blob monitoring OFF, the crashing is minimized dramatically.
I'm not happy that I can't monitor when I click and drag, but at least sonar isn't crashing with almost every attempt to create a Melodyne region.
Give it a try and see if it minimizes it for you as well.
The stand alone version of melodyne appears to be working.
It's the interaction with Sonar that is screwed up.

I wonder how many of you having problems are using a different sample rate, or possibly a something different than 44.1 kHz ?
 
Chuckebaby, I use also 24-bit 44.1 kHz, but nonetheless I had a lot of crashes with Melodyne the last time (about a dozen automatic crash reports are sent to the development). So I began to save frequently in between and I found out that if I do switch a little slower from Melodyne to Sonar (e.g. play button), then there are almost no crashes anymore. I think it could have something to do with the audio driver in my case, because most of the time it was during playing or when I started playing.

Just to add to the chorus, Melodyne 4 is a huge pain and unstable as heck.  I found it impossible to roll back to the older version.  After mucking around and reading this thread, freezing any instance of melodyne isn't enough:  I have to delete the offending track after bouncing. Spent three hours this morning figuring that out.
 
For me, Melodyne has been banished from inclusion in any main project file.  I use it on a separate file and then import the audio into the main project.  Celemony support has been unhelpful.  Stay away if you can.
 
 

I must be lucky...  Melodyne 4 has been working fairly well here.  Granted, I do bounce the clips when I'm done editing, but just for kicks I did leave 3-4 instances "live" thru multiple sessions but still didn't have any crashes.    There must something in common between those having this issue vs. those that are not...
 

Yeah, it's a mystery. 100% repeatable in my case, unfortunately.