Hi
I’m experiencing the same problem.
I tried moving the unwanted downstream selections to a different audio track on the timeline.
Which stopped them being selected with the upstream forward tracks selection but then final cut decided to select other downstream clips instead. They seem to be random, there’s no apparent correlation with the upstream footage in any way.
I’m also working on a feature length documentary.
I’m wondering if you done any media management before this problem started?
“Don’t let the behaviour of software destroy your inner peace” adapted from a quote by his Holiness the 14th Dalai Lama