Alright, whilst mixing a collab, I've encountered an issue, one which I've never had before. There are 4 seperate WAV files of guitars - Track 1 - Track 1 Double - Track 2 - Track 2 Double. Track 1 and Track 1 double both have no issue when VSTs are mounted on to them. I'm using Simple Guitar Combo from Nick Crow, and Kefir Impulse loader. However, when I attempt to mount most VSTs onto the tracks with Track 2 and Track 2 double, the track plays back but with no sound. I've tried searching for this on google, and i haven't been able to find anything on it. If you need to know which version of REAPER I am using, I can get this for you,
There's a special sex move I do called the Charizard.
It's where you light the girls pubes, then put it out with your cum and run around the room flapping your arms screaming, "You don't have enough badges to train me!"
This may not help but here goes:

Save the dry tracks for later reamping, then once you've got the individual track FX set how you want, mix those single tracks down to separate WAV files in a folder for your current project. I started doing this out of habit years ago as a way to cut down on CPU usage and it also simplifies adding EQ, etc to each track as you don't have to navigate through the FX you already have on the tracks. It sounds like you're just eating too much RAM, but that may not be the case and it may just be a glitch or something. Hope this helps