Normally, when playing back video through the WS software, playback will skip over any gaps in the recording.
When an NSM5200 system is set-up with a Failover NSM5200 and parts of the video are recorded on the Failover NSM5200, the WS will skip over the Failover NSM5200's video and not take it into account.
Pelco Video Management
Right now, this is the way the workstation software operates; there is no workaround for this. Cause is most likely that the failover NSM is outside the normal pool and is not being controlled by an NSM5200 manager so its video as seen as another source by the workstation software.
Just keep in mind this is how the 'play through gaps' feature works when using a failover NSM5200.