Hmm- it sounds like the capture device is to blame here and guessing on the age of the thing I’m suspecting an update for FCP X compatibility is not too likely.
Post some inspector snapshots of the clips. FCPX supports a lot of formats but it’s quite possible to create a format that it doesn’t support, especially with older gear.
Yeah are you sure you haven’t just added color corrections? The thumbnails on the timeline do not update to reflect changes to colors you make in the viewer.
Did that clip come in via Firewire directly from a camera or was it rendered someplace else? What was used to ingest the original clip- FCPX or another app?