Did you try all the steps in post #4 (inc #9) and all the steps in #15?
This may save your a support call they are likely to ask similar sorts of questions...
 
Otherwise...
 
If I hazard a guess it would be somehow related to this (totally different steps and totally different behaviour):
http://forum.cakewalk.com/Jamaica-Plain-heavy-performance-problems-m3303385.aspx
 
Complete speculation however I can't back it up, could very easily be wrong.

Yes, I've tried those steps. Am trying the 'scan on startup' currently. I'm not getting the CPU spike though, and the arm thing is not checked anyway. - although I don't know how to get the wave plugins out of the way. They haven't been a problem previously so I don't understand why suddenly they're an issue...they scanned ok in previous versions.
 
I suppose I could take the path out of the vst scan, but then they wouldn't be scanned properly and it just become too complicated.

You need to note the file path/s in Sonar listed in Preferences/VST Settings, then open them up in Windows explorer.
You should see a list of DLL's.
When the scan stalls you should be able to work out which DLL is it from the filename.
Simply move the problem DLL somewhere else (say a folder on your desktop).
Keep moving problem DLL's until scan completes (you may need to restart the scan or restart Sonar each time after you do a move).
After that you will end up with a list of effected DLL's. It may only be two or three.
Try the scan again (do a reset again) to see if there are no further issues.
When you've finished you could move them back (back to stage 1), or choose not for the meantime (so you have a working system).

Post them here if you like, knowing which plugins are having problems may at least help diagnose the specific issue, and the info will be useful to cakewalk at least. For instance you may find it's just the wave plugins effected.

As a sidenote I WISH we didn't have to do this. It would be much better if the plugins that were not working were skipped and an error report generated at the end of the scan. Would make life so much easier, don't know if this is possible or not.

Doktor Avalanche
You need to note the file path/s in Sonar listed in Preferences/VST Settings, then open them up in Windows explorer.
You should see a list of DLL's.
When the scan stalls you should be able to work out which DLL is it from the filename.
Simply move the problem DLL somewhere else (say a folder on your desktop).
Keep moving problem DLL's until scan completes (you may need to restart the scan or restart Sonar each time after you do a move).
After that you will end up with a list of effected DLL's. It may only be two or three.
Try the scan again (do a reset again) to see if there are no further issues.
When you've finished you could move them back (back to stage 1), or choose not for the meantime (so you have a working system).

Post them here if you like, knowing which plugins are having problems may at least help diagnose the specific issue, and the info will be useful to cakewalk at least. For instance you may find it's just the wave plugins effected.

 Thanks but it doesn't work like this for Wave plug-ins. 
And no, I don't think it's a plug-in issue at all. I think it's something to do with the upscale playback in real time. For example, after doing the scan at startup, Xpand!2 vst was 'sort of playing' the line I had recorded...hit or miss really, 8/10 it would start with playback. After selecting upscale render in real time, it was completely off and 'sometimes' starting several seconds into the project. 
 
I haven't time to stuff around with this. I'm rolling back until Cake can sort it out. Very disappointed but you get that.

Fabio Rubato
 
Thanks but it doesn't work like this for Wave plug-ins.

 
Not understanding sorry, VST files are just DLL's. There may be other related files around it but they should stop working when you remove the main DLL. Happy to be corrected.
 

Fabio Rubato
And no, I don't think it's a plug-in issue at all. I think it's something to do with the upscale playback in real time. For example, after doing the scan at startup, Xpand!2 vst was 'sort of playing' the line I had recorded...hit or miss really, 8/10 it would start with playback. After selecting upscale render in real time, it was completely off and 'sometimes' starting several seconds into the project. 

 
Yup see your point, but it may be specific plugins that are effected here, really useful information to know. I very much doubt it's all plugins.
 

Fabio Rubato
I haven't time to stuff around with this. I'm rolling back until Cake can sort it out. Very disappointed but you get that.

Totally understood. Hopefully somebody else will report the specific issue or they will stumble across it, or maybe they will locate the cause the problem via some other means.
 
Cheers..

After updating to Jamaica I noticed I was missing waves plugins in my vst3 directory so I did a rescan & got a hang on a waves plug also. So I rescanned again only this time I unchecked "rescan failed plugins"/rescanned/and all my waves plugins scanned correctly.

stlstudio
After updating to Jamaica I noticed I was missing waves plugins in my vst3 directory so I did a rescan & got a hang on a waves plug also. So I rescanned again only this time I unchecked "rescan failed plugins"/rescanned/and all my waves plugins scanned correctly.

Okay, thanks for that. I could try that, but I'm not sure at this point whether it's going to fix the issue with a number of VST softsynths that are starting late and continuing to play once the project has stopped. I've installed Jamaica and un-installed around 4 times now, so I'm going to wait until tech support contacts me, which will probably be 2 weeks done the line, based on past experience. 
 
Again, thanks for that. I assume you're not getting any weird timing delays with your soft synths?

It does look like he forums is littered with waves issues all of a sudden.
http://forum.cakewalk.com/tm.aspx?m=3304786

Fabio Rubato

stlstudio
After updating to Jamaica I noticed I was missing waves plugins in my vst3 directory so I did a rescan & got a hang on a waves plug also. So I rescanned again only this time I unchecked "rescan failed plugins"/rescanned/and all my waves plugins scanned correctly.

Okay, thanks for that. I could try that, but I'm not sure at this point whether it's going to fix the issue with a number of VST softsynths that are starting late and continuing to play once the project has stopped. I've installed Jamaica and un-installed around 4 times now, so I'm going to wait until tech support contacts me, which will probably be 2 weeks done the line, based on past experience. 
 
Again, thanks for that. I assume you're not getting any weird timing delays with your soft synths?

Fabio, in your options, midi/playback and recording, what is your playback set to? Default for playback is 250...if you have yours set to that, what happens if you try 500, 800, 1000 or even 2000?
 
One of my machines is set to 800 as I had some drop outs using hardware synths years ago, so I never touched them. The other two were 1000 and 2000. Those numbers just seemed to work where I never had an issue with anything.
 
On one of my machines, setting that option to 500 sort of cured my synth problem to where it will work great for the duration of the project being open. As soon as the project closes and I close Sonar and reopen, the sync issue is back...but all I have to do is start/stop playback and the sync issue is gone again.
 
That said, on my other two machines....I am unable to make it stop no matter what I try. I'll keep looking into this and let you know if I figure anything out. I'm going to try and contact Cakewalk to see if they know anything also.
 
-Danny