OC Strings is always fine for me - loads up every time, no problem. Even loading 4 of 5 instances at once, it's surprisingly lightweight given that you get 7 or 8 gbs of content. I can't think of any other VSTi's just NOT loading or having trouble loading besides Xpand.
I've got a sort of orchestral template with no fewer than 4 instances of Xpand - takes FOREVER to load, sometimes DOESN'T load, etc. But that's a combination of poor planning and low-level system. Xpand isn't the most lightweight thing out there, but it does so darned well that it's worth keeping around.
With Xpand, I generally don't do any patch changes at all, one patch per MIDI track, four MIDI tracks per instance of the plugin.
But like you mentioned, abacab, I use Xpand a *lot* with imported MIDI files and often times I end up with {many MIDI tracks that already have a patch or bank setting on the MIDI track's properties.
I'll look into maybe some leftover patch changes from Sibelius - but often times, if I try to set the bank or patch afterwards (to sort of default them to blank settings in the MIDI tracks), the patches resetting in Xpand becomes a bit of a problem.
But I've so far had BIGGER problems when I had stuff where I was saving custom patches inside Xpand. I was working on a rock tune where I had an organ, two guitars and a bass in Xpand, and because it defaulted all four patches twice, I saved the patch in Xpand and just loaded it up every time, saving right after I made changes every time.
I looked back through the MIDI tracks and there were no traces of patches changes in the MIDI clips, so I chalk it up to messing around too mucch with patch/bank controls on the tracks' individual controls. Not sure how to set them so that they don't "move" or do anything weird, but also don't look like they'll randomly change to something else because they're not all "defaulted".
that was a lot :3