My guess is that as far as Premiere is concerned you have used loads of different video clips instead of just three.

By importing the same clip multiple times, into different 'bins', I suspect Premiere does not 'remember' it is the same file at all and has simply conformed the audio for each instance.

I suggest you remove all duplicate imports anmd just have one version of each clip imported. You should then just have one conformed audio for each clip.

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