This could be due to a number of factors, one of the primary ones being the missile and target veered away from each other so the seeker wouldn’t see them, however as it stands ingame the seeker will turn on once it gets to the last known position of target (the circle on radar) and search for any targets within ~4 km of itself within its gimbal limit.
Obviously if you maintain lock this isn’t an issue as it is continuously updated but if it’s dropped or they start notching before and disappear then the missile will fly to that spot, turn radar on and then search and attempt to destroy the first thing it sees
Pertaining to the RWR thing: entirely true. It is effectively a nerf, as the tiny, underpowered radars in missiles will struggle to see let alone track a stealth fighter on its own reliably. It needs continuous updates from the mothership to hit anything. In the event that it does, it would have likely been guiding in via IOG+DL and would’ve been trying to acquire a lock itself over time but couldn’t. The missile getting closer is what leads to “last second” warnings on RWR, especially for stealth fighters.
Maybe a few kg of that is, but the rest has to either be a different motor or just more fuel. No way a bigger battery or GPS guidance is that heavy lol