Hello, this is kind of a long winded question, and I suspect that the answer is - you are working on a four year old documentary with countless sources some of which were downloaded from the internet, and some of which may be slightly corrupted.
I have recently found that, in certain clips, the left and right audio channels seem to be linked to specific track numbers.
For example, even when I drag the audio down from the source, what was formerly a stereo track will be panned to the left or right channel. Modifying the pan in FCP does nothing to fix this. Even unlinking the pair and modifying them individually (which is an absurd fix) does not help in some cases.
It was by chance that I realized a pattern, in some cases the left channel would play on tracks five and six and the right on track ten and eleven.
My hope is that a mysterious setting got changed, my fear is that I will have to proceed with band aids.
These clips are all pal video with stereo sound, and the problem seems to have cropped up recently. The project was saved from itself several times, recently I pasted the timeline into a new project because FCP kept crashing.
Did you check the audio configuration in your sequence setting? It sounds like they got switched from "stereo" output to discrete mono output. Open the sequence in question, then hit "command-zero" to access the sequence's settings.
Thanks so much, the sequence was set to "Channel Grouped" and I have changed it to "Stereo Mixdown." It seems now I have to drag the tracks down from the original clips in most cases, it also still works to just move tracks to 5 & 6, so some work to do to fix things up, but I this is a much better solution that what I had been doing up until now. Any other time saving advice much appreciated, otherwise thank you so much !