The reticle lock goes away completely as soon as the crosshair is off the target, even for less than a second. With other weapons, the reticle will gradually unlock, but you can reacquire the lock quickly, but with drones, you have to start all over again and wait for it to close.
It's always done that with drones since they got a reticule. Dont know if it is intended behaviour though. If you get a lock on one target though, you can move onto another one when they overlap and keep the lock aswell.
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