This is all anecdotal and based only on my experience, but I'm going to post it here anyway.
From flying the campaign I also have felt the behavior of the Vikhr has changed from FC2 to World. I have been loosing a lot of missiles that just seem to fall off the beam and nose dive.
For a test I tossed together a .miz with 1 toad and 16 targets. From range, at altitude, and speed, I have gone 16 for 16 hits, all 3 times I've flown it.
This leads me to believe the behavior differences we pilots keep seeing and trying to report has to do with low level, low angle, slower speed attack runs.