Hi Michael,
Most of these problems are due to users not importing footage properly.
Copy the entire card and its file structure to your media drive.
Ingest the files via the Media Browser NOT via File > Import or by dragging the files into the Project panel.
Do NOT do the following if you have AVCHD footage:
Update the project file mid-way through your project.
Update the OS mid-way through the project.
If AVCHD files get red frames or go offline, do the following:
Change the name of the media files folder
Delete the Media Cache
Relink the clips in any existing sequences.
Thanks,
Kevin
https://forums.adobe.com/thread/1505098