The fact that you can run older versions without a problem could be indicative of something else that needs to be updated. This isn't far fetched from the issues people have with this forum version and FireFox. At some point Sonar probably has some code tweaked/optimized, or removed to save some space, but lowers tolerance to something else running that isn't 100% supported.
Don't rule out a full re-install of X2a. This helped me minimize some crashes. Remove X2a, then do all the updates you can find for existing hardware and the OS, reboot, then re-install X2a. Then re-scan for plug-ins. I've certainly found some improvements in the re-install. Be sure to include Visual C++ Redistributable as one of the updates, as Cakewalk has offered this recommendation for Waves Plug-Ins locking up the DAW.
Hope this helps!!
Brian
Sonar Platinum, Steinberg Wavelab Pro 9, MOTU 24CoreIO w/ low-slew OP-AMP mods and BLA external clock, True P8, Audient ASP008, API 512c, Chandler Germ500, Summit 2ba-221, GAP Pre-73, Peluso 22251, Peluso 2247LE, Mackie HR824, Polk Audio SRS-SDA 2.3tl w/upgraded Soniccraft crossovers and Goertz cables, powered by Pass-X350. All wiring Star-Quad XLR or Monster Cable. Power by Monster Power Signature AVS2000 voltage stabilizer and Signature Pro Power 5100 PowerCenter on a 20A isolation shielded circuit.