logic x 10.4.1 - Stereo imbalance wave bounce

Hi,

When I bounce my track as an mp3 the left and right stereo of my track is level but when I bounce it in Wav form there is roughly a 5db difference in the channels. It is starting to drive me insane.

Top audio is the mp3 and bottom is the wav.

Now the strange thing is it only happens around 2:45 mins into the track

If i bounce the track from 2:45 onwards it doesn't boost the other channel. Could it be a problem with the 10.4.1 update? I hope it is something stupid as I only have another week before I have to send the track off.

Thanks in advance.