Dahua NVR2104H Empty Recording

[Prav]

Hi I have Dahua 4MP IPC-HDBW4433R-ZS connected to Dahua NVR2104H. During playback, I noticed that when heaps of motions are detected (solid yellow lines/rectangle) there is a 3 minute gap (grey) after but green after single MDs.
Any ideas why?
Thanks.

Edit: On NVR, this pops up. "10.1.1.65 Cannot find the network host" when constant MDs are recorded.