XML issues FCP7 multiple video tracks to Resolve

I recently had a documentary job presented to me for grading which had been media managed in FCP7 by an editor with minimal experience.
The media included Prores, mp4, mp3, wav, aif, H264, jpg, png & tiff files.
Project was 1080i 25fps.
The media managed timeline was 4 video layers with transitions and effects on many clips.
The xml files had also been created by the editor.

The xml file imported into Resolve ok, but some unsupported media was not imported into the media pool.
The grade went well and I did the usual round trip render with the same handles as provided by the media manage in FCP7.

When importing the new xml back into FCP7, all effects and transitions were missing.
I did many hours of testing to determine why this was happening. It usually works perfectly.

The solution that worked was to create a separate timeline for each video track in FCP7, then export the xml for those new sequences into Resolve. I then used ColorTrace to match back the grades from my original graded timeline.

I then rendered out the new graded timelines to separate media folders and re-imported the four xml files back into FCP7. Then I copied and pasted the sequences together to re-create the original timeline.

For some reason all the effects and transitions worked perfectly using a round trip with only one video track exported from FCP7. If I tried to export all four tracks the round trip lost all the effects and transitions.

Interestingly, if I exported the original sequence with 4 layers using a FCPX xml file the project imported perfectly into FCPX. No loss of transitions but of course, incompatible effects. Also no good for my client.

I hope this information may be useful to someone.

This is the reason why I modify my workflow - when I can decide, i.e. when the whole project is not given to me at the end of post-prod - in order to :

- anticipate whatever problems might happen with multi tracks projects
- spare fixing time, especially trying to get transitions or effects back on TL

I consequently export a "cuts only" XML to Resolve, with almost no transition and no effects > grade > round trip back > add transitions and effects when back in NLE

I know this is a bit of a pain in the ass, but if you know you're going to, it can be easy...
In the meantime, I'm a bit afraid about BMD possibly not motivated to improve XML side but only FCPX XML... (which is precisely pointless for those who decided to "replace" FCPX by Resolve)