Kollector Strike Issue

[tcon001]

We were reviewing footage on a Kollector Strike.  Previously the footage was present and now it is gone.  I can look at the timeline on playback and see the gaps where the footage is missing.  My thought was the DVR was down at that time but as I said the footage was there and viewed previously.  Now it is just missing.  Any clue what happened here and what's the possibility or recovering the footage?

Thanks,

Raymond E. Conrad III