Yep, I'm having the exact same issue in the campaign for the SU-25T.
-Confirmed my Shkval was properly locked onto the target
-Aircraft was kept steady (didn't make any sudden or side-to-side movements)
-LR was active
-Target was in the center of the Vikhr reticle
-I maintain target lock and position of the aircraft
Not sure what I'm doing wrong. Though as the OP pointed out, for some reason my reticle is to the far right of the HUD (I don't know what this suggests...). About 4 seconds missile launch, the missile just plummets to the ground, falling short of the target.
In the custom missions I've created, I've only encountered it once or twice. Seems to happen half of the time for me in the campaign...
Anyone have any ideas?
Thanks!