xml to otio flattern bug issue

Hello,
I am reading the edited xml file with otio and flattening it. When I read a certain xml file, I confirmed that otio is properly created, but when I try flatten, the data disappears. Is there a way to debug this situation?

[Battle_Edit01g_S009-018_edl.xml.zip](https://github.com/PixarAnimationStudios/OpenTimelineIO/files/4247623/Battle_Edit01g_S009-018_edl.xml.zip)

Start by reproducing the report with the attached Battle_Edit01g_S009-018_edl.xml.zip file: read the edited XML into OTIO and run flattening while inspecting where the data disappears. Trace the XML-to-OTIO import and flattening entry points; done means the supplied XML remains intact after flattening, or the failure is documented with a focused reproduction.

Written by the indexing model from the issue text.