Zorro23

It happened to me as well on multiplayer at least twice about a week ago. I was at 40k ft with hard-lock on target at 4k ft head on. When I was about to fire at about 14nm I lost my lock. I tried to regain lock on them but even following closely the AWACS indications they never show up again on the VTB. So after a 180° turn I tried again (this time I was at their six) with no success. Then even the AWACS lost them and when I managed to lose altitude a SAM shot me down.

UP not yet :(

Theoretically this behavior is correct. It's one drawback of delta wings which suffer high drag (and so velocity loss) at high angle of attack due to the huge tip vortexes.