Bomber master is... NOT glitched.
Because I just got it!
You can do it on any difficulty (So do it in free mission with the lowest setting), you have to do it on the mission where you control the bomber and are dropping what feels like a million bombs onto the ICBM base.
How I got it though... is another question.
The trophy popped up after I beat the base which prompts the MIG's to come.
This suggests that it's logging your kills at the very least upto checkpoints.
I've played through the stage twice in full, this time was my third attempt before I hit that checkpoint.
However I had failed to hit some ICBM's a few times which prompts a restart from the entire bombing run.
The only advice I can offer is to do the entire mission in free mission mode with the difficulty set to it's lowest setting, the number of enemies does not decrease with difficulty.
As for how many 'perfect' runs it will take you... urm... honestly? I have no idea.
But just keep replaying this stage and it will pop up.
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