I'm seeing some UAD problems in X3c. 
 
I have had FX Send processors seem to lose their delay compensation so that I hear a slightly delayed repetition of things.
 
I have had an 1176 stop processing sound, but still pass audio along.
 
One or two other things perhaps, can't remember.  Of course there's the "-26 other plugin between two UAD plugins" error which seems to simply be something UA has to release a fix for, although they failed to do so in the latest update.  I'm not sure if that's something Cakewalk can also address...
 
What else have people noticed?  It would be good to know what kind of things can go wrong in case I get some new problems.
 
What's the word from Cakewalk about this?

 For some reason I was still having the same issues with the new 7.4.0 11-14-2013 build 5589 driver, as I was having with the previous driver until I did a VST rescan.
 After the rescan the error about other non UAD plugins went away and so far no other issues with it. 

This thread details my problems with UAD-2 and Sonar X3. http://forum.cakewalk.com/Lovin-X3-But-Not-UAD-m2911112.aspx
 
Upgrading to X3c has made no improvement, but since filing reports with both UA and Cakewalk, each has contacted me, saying they are aware of UAD/Sonar problems, and offering suggestions. Unfortunately, their suggestions haven't worked, and after being informed of that, each has replied that they are working on the solution for a future update.

So, what I had to do was completely uninstall UAD... then I erased all folders with UAD plugins and reinstalled UAD (which puts the plugins into the STEINBERG folder under programs)... go back into SONAR and plugin manager and rescan making sure the aforementioned STEINBERG folder was in the folders to scan list.
 
This seems to fixed MOST of the problems with UAD and SONAR.
 
Jim
 

If you toggle the FX button when that occurs, it goes away. Annoying but simple fix for now.  You don't have to reinstall  anything if you can live with that and for me it only happens sometimes.  I use a lot of UAD and waves intermingled and this works every time (for me)   Also you can try closing and reopening the project (or Sonar overall)  which sometimes helps as well.

Toggling the global FX button on the toolbar does nothing with the UAD plug-ins in my system. Toggling the button next to the individual plug-in in the effects bin temporarily causes the plug-in to start processing audio properly...but the moment the transport is stopped, it quits working again upon hitting PLAY. This means I can listen to the project with a plug-in active, but since it resets to not working upon hitting STOP, there is no way to export a mix with UAD plug-ins active.

I experienced this problem for the first time in a session last night.  I found that toggling the button off & on in the FX bin helped, but when you open the session again, the problem is back... This is actually the first time I have experienced any problem with UAD in Sonar.

Today I'm getting a problem where reverb (for example) in the fx send stops effecting the sound if I add a UAD plugin to the track sending to it.  Turning it on and off in the bin fixes it.  I would guess that it's an issue with delay compensation given the added latency the UA fx incur.
 
What's the word on when the next update will come out?  Cakewalk was pretty active on the forum for a while talking about X3d and apparently aware that there were unresolved issues with UAD fx, but there's been nothing for weeks now. 

I also rescind my earlier claim that the reinstall fixed my issues with UAD and X3.... I too am having the problem wherein the plugin STOPS to work but passes on audio unprocessed.  Toggling the on/off button within the bin seems to clear up the issue.
 
I hope somebody addresses this soon and I think it is on the UAD side if I remember reading other posts concerning this dilemma.
 
Jim

I wouldn't be surprised if its a UA problem, although Cakewalk must have done something to get it to work in X2, which had none of these problems...