The thing is IMHO, Reaper is really very sensitive regarding VSTi usage & tweaking. I can run most any VSTi here for a few days without any problem but then one minute later ANY VSTi can crash Reaper while tweaking any knob. I've had quite a few crashes already, always with different VSTi's and never under the same condition or reproducible.
Unfortunately
And I don't even try out heavy projects yet with Reaper. The biggest I had running was about 6-8 audio tracks (guitars & drums) and 2 or 3 VSTi's at the same time.
Raphael