Yes, indeed this happens once your memory usage in the project increases to a certain point.
I've found that once ANY project is using somewhere over 3GB, or approaching 4GB, this happens to R-Mix all the time, and basically becomes unusable in the project.
Projects with a small memory footprint, it works fine. But as the project grows, you'll reach a point where the R-Mix GUI is jst about always blank and it becomes unusable.
You can confirm the problem is related to the memory footprint of the project, simply by creating a new project, add a few small audio tracks, and insert R-Mix - it should work fine, so long as the memory footprint of the sonar process is small.
I can start a new project, insert half a dozen instances of R-Mix, then add content to grow the memory until R-Mix becomes unusable. 100% repeatable.
Please log a problem report at cakewalk.
I've logged a problem report weeks ago, but haven't had any response back at all.
If I don't hear back in another week, I'm going to write something up and start logging problem reports every other day until I get some type of response.
BTW, I'm using X2a, only the 64bit version - I'm not intending to install 32-bit stuff any more.
Cheers - Cliff