Ok, I have tried transcoding all to prores, and again, doing the exports both as protools, and the AVID AAF options. Also tried exporting FCP XMLs and importing them into FCPX / LogicPro and that produces the wrong results (missing sections). The project originated as an FCP 7 project which I imported into Davinci Resolve to do the sound mixing / dialog. I went back to the original FCP 7 project, did an OMF export and that has imported into Nuendo absolutely perfectly. I therefore think this is a Davinci Resolve issue. Sadly though, I have edits in Davinci Resolve which are using synced audio clips so really want to get resolve => external DAW working.