Town Hall recording missed most screen sharing

We hosted a conference using Town Halls and then reviewed the recordings, which we intended to share with people who missed the conference. Most of the screen shares that happened during the event are missing from the recordings, but not all. We don't see any pattern as to who's screen shares made it into the recording and who's didn't. One presenter had half of their presentation recorded, and half missed. The audio is fine throughout.

There was no indication of any problem during the event, and no warning that any content would not be recorded.  This is totally unacceptable, because the recordings are now unusable and we can't repeat the event. 

Has anyone else had similar problem?  Do you know what caused it and how to avoid it?