Frustration greeter
A dog that lunges and screams at other dogs because it desperately wants to reach them, not because it wants them gone.
Also called: he's friendly · barrier frustration · wants to say hi
From two metres away this is indistinguishable from aggression, and it is regularly treated as aggression, which is how a sociable dog ends up frightened of the thing it used to love.
The giveaway is what happens on arrival. A frustrated greeter that finally reaches the other dog is delighted; a fearful one is not. The body is looser, the tail is high and fast, the noise is higher-pitched.
The fix is close to the opposite of the fearful plan: the dog learns that calm is what opens the door, and that the lead is not a permanent barrier to everything good.