I'm still confused on the exact issue but the Cakewalk engine will stop if you change the ASIO buffer size in mix control. Perfectly normal, Sonar will pick it up and you can continue as normal after that. I dont think you can change it whilst playing. If you have different behaviour with these mix control settings then look at #4. In fact I routinely perform a reset and full uninstall/reinstall everytime I upgrade mix control as I have run into too many upgrade issues with this software.

Mosvalve
The record i/o buffer size in Sonar "preference sync and caching" does reflect the ASIO buffers.

This is incorrect. The value has nothing to do with the ASIO buffers, never has in SONAR. ASIO buffers are between the audio interface and the DAW software, the record and plackback buffers in Preferences > Audio > Sync and Caching are between the DAW and the disk. The disk buffers have always been manually set in every version of SONAR I have owned. The client software for an audio interface would not even be aware of the disk buffer settings in SONAR. Just to test this, I altered the ASIO buffer from 128 to 1024 and while the mix latency setting reflected the change in Preference > Audio > Driver Settings, the playback and record I/O in Preferences > Audio > Sync and Caching remained unchanged in X1 Producer Expanded, X2 Producer and X3 Producer, the only versions installed on my current machine.

I stand corrected. Preference>Audio>Driver settings>, that's where it changes in Sonar when changing ASIO buffers in mix control. I was looking in the wrong place. My bad. All is well, nothing broken except me. Thanks all for clearing this up for me. Sorry for the confusion and appreciate your help.