I’ve been having consistent issues with Sparrows in aircraft that use the AN/APG-66 (specifically the F-16AJ and the F-4EJ Kai) where I have a solid continuous lock on a target within near-optimal parameters (head-on, at altitude, not maneuvering or chaffing, missile indicator fully positive) but the AIM-7 will still completely ignore it and fly off in a random direction, sometimes even doing a full 180 turn.
I’ve also had instances where I would launch 2 missiles at a locked target, and both would go towards to two other completely different targets, nowhere near the currently locked one, and killing both of them, essentially turning the AIM-7 into a semi-Fox-3.
It’s a coin toss if it happens or not. It’s the only radar that’s making them act like this. No other aircraft with AIM-7s does this, even the AIM-7D on the F-4C tracks more consistently.