loss of quality when exporting iPhone HDR footage!

When exporting the project I did see a warning on the main screen before the export but I could not figure out what it was and it did not give me any details. When watching in FCP the footage was perfect, so I exported it and then uploaded directly to yoututbe. Since publishing the footage it is severely low contrast and saturation and honestly looks terrible.

But because I have never had an issue before; I did as I always do and delete all the files and footage to make room for the next project.

But moving forward what issues can cause this when exporting because I now have a project with iPhone footage getting the same warning message.

This is so frustrating to spend so much time on a project just to run into issues like this. I feel like every few months it's something else after a major update that just puts a kink in the work flow because something has changed and not for the better. That was a 25 min exported project that took even longer to film and get correct.