tnipe
I also experience issues with latency on parallel compression auxes when 2x oversampling is enabled. I emailed support about a month ago, but no reply so far. I get this now and then without 2x enabled also, but it usually goes away by stopping and starting playback again.

Indeed, 2x oversampling is enabled on Fabfilter pro L on my " Wet Drums Bus ".
I wasn't aware about this issue.

J-War

tnipe
I also experience issues with latency on parallel compression auxes when 2x oversampling is enabled. I emailed support about a month ago, but no reply so far. I get this now and then without 2x enabled also, but it usually goes away by stopping and starting playback again.

Indeed, 2x oversampling is enabled on Fabfilter pro L on my " Wet Drums Bus ".
I wasn't aware about this issue.

Does disabling oversampling resolve the issue?

This is just a workaround. 
I would bounce the "Dry bus" and "Wet bus" to tracks. Then they can be moved into alignment and the project can be finished.
At the least you can determine how many samples off the resulting tracks are.

One thing that's worth knowing about Sonar is that it does not have gapless playback, so doing things like turning stuff off and on during playback will often cause glitches and delays. One of these problems is that if you enable a send during playback, it will be out of phase. I get this all the time with parallel processing. It also sometimes happens when you have a loop enabled - I used to have a huge problem with using MarkBass on a send because it would always go out of phase upon the first iteration of a loop. So now I also make sure to stop playback before enabling a send.

So all you have on the parallel bus is the CA-2A? What's on the primary drum bus?
 
BTW, this doesn't solve the mystery, but you could avoid all this by using a different compressor. Since you're a FabFilter guy...would you happen to have Pro-C?

Might this be relevant to your situation?  I'm not sure how your limiter plugin is configured on the parallel bus and I'm not familiar with the plugin.  You say "Waves SSL Comp Stereo" so this might not be the issue, but if the limiter is configured as a mono VST...
 
Using mono VST plug-ins on stereo tracks may cause out of sync audio -
When using a mono VST plug-in on a stereo track (interleave set to Stereo), the left and right channels will be out of sync. The left channel is processed by the mono effect, and delay compensation is applied, while the right channel is not processed and does not have delay compensation applied. The signal will look something like this:

• Left channel: Wet signal (delayed)
• Right channel: Dry signal (no delay)