I have been monitoring a camera that has activity over the day. The recording appears in the clips as expected. Occasionally during the day I review the recording. Sometimes the first portion of the recording gets lost. Any suggestions about why this could happen?

Are you saying the part with the actual motion detected is no longer there ? What if you look in the Clip files ? Is the missing video there ?

I have found the reason for the video file deletion: I had Blue Iris Settings | Storage | Folders configured incorrectly.