Redirected to this thread from another, although my issues are with Melodyne 4 Studio, not Essential.
 
My limited experience confirms the issue is with split -and edited- clips. I can successfully apply 4 Studio as RFX to both clips of a split clip in the same take lane and to clips in multiple take lines -IF- I do not drag the clip boundaries or move them. If I drag a clip boundary or move it, applying 4 Studio as RFX will crash Sonar.
 
FWIW, I pinged Celemony on the reported issues before upgrading and was assured of the following;
1. backwards compatible with V2 Editor clips
- "We paid attention to backwards compatibility"
2. x64 not as stable as x32
- 64 bit "is even recommended"
3. ARA performance not as 'capable/efficient' as standalone performance.
- "ARA currently does not allow multitrack editing."
 
Perhaps split clips are interpreted as multitrack by Melodyne?
 
I will follow up with Celemony as it is their product that crashes Sonar but some attention/priority/influence from Cakewalk appears to be in order as they were promoting the latest version of Melodyne and is not compatible with a fundamental feature of Sonar.
 
My recommendation is to stick with Melodyne 2 Editor until this gets fixed.
 
<specs for test platform>
Sonar Pt 2016.03 / Melodyne 4 Studio 4.0.4.001 vst3 x64 / Win10 Pro fully updated / x64 / i5820k / 32GB

For anyone experiencing this problem, if you first use the Trim command on all clips you want to simultaneously use with Meldoyne/ARA, does the error still occur?
 
 

After upgrading to 2016.4, I was actually able to create 2 or 3 (in one case 4) region FX, but the system still would inevitably crash each time.
Tonight, I will try reinstalling Melodyne with the new SPLAT. I will try 32 and 64 variations (the 32 bit install 'workaround' didn't work for me on 2016.3)
Also, when the region effects were created, after editing, I could still hear the unedited vocal along with the edited vocal...
Just a FYI on my experiences, and a way to hopefully keep this thread alive until resolution :)
 

Thanks for the report.
 
Viva la resistance!

I have had melodyne issues in the past. I have not had any yet in 4, knock on wood. I ALWAYS set buffers at 1024 before doing anything with it. So much so, that I have a note pasted on the bottom of my monitor. I paraphrase: "before doing anything in melodyne, save, close, and exit Sonar, adjust buffers to 1024 , open and resume work." PITA? You bet, but not nearly as much of one as having the damned thing crash.Interstingly enough, my problems often seem to occur if I try to reset buffers " on the fly".( that's probably more an interface issue than anything, but why tempt the fates.)

I too experienced several crashing issues with previous versions of Melodyne and SONAR. What ended up working for me was bouncing the Melodyne-corrected clip to a new track then deleting Melodyne entirely, as the crashes would often occur when attempting to open a project with Melodyne active. The other crashes occurred when attempting to create a Region FX.
 
I couldn't resist the cheap upgrade to the Studio version of Melodyne so I bit the bullet, and thus far, I haven't had any issues with SONAR Platinum and Melodyne 4. However, my workflow has changed: I never use Region FX for Melodyne anymore. Too much instability in the past, so now I insert Melodyne as a plugin, capture the performance in real time, then go from there.  Luckily, thus far, I haven't gotten any crashes, even with the plugin active in the FX Bin. We'll see if it holds up.
 
I'm using the 64-bit version.

Melodyne crashes SONAR every time I try to create a second RegionFX. I hope that Cakewalk will find a solution.

Just wanted to give an update on this.
We had sent the fault reporter crash dumps we received to Celemony, they are looking into it.
Thanks for those that sent them in.  

Thank you for the update Keith :)

I'm having the same problem with Studio 4.  It's the first time I've had Platinum crash.  It sent error reports twice.  I had to use Studio 4 in stand alone mode to be able to use it at all.