Don't know it it keeps working, but - for now - that tips seems to help this problem too:
I have a Dahua IPC-HDW5231R-ZE and a NVR4116HS-4KS2. I records IVS/tripwire events on a SD-card in the camera and the NVR records 24/7 and IVS events. Or it should. Every once in a while, the NVR stops highlighting/recording the IVS events; it just shows the 24/7/general recording green bar...
www.ipcamtalk.com
IVS didn't show up on the NVR's timeline again today. (apparently not since last Thursday). Did the above and now working again.
But still, this shouldn't happen. I'm lucky I'm using SD-cards in the camera's (where I'm only recording IVS events), otherwise I wouldn't known what happened.
But I think it's something to do with my IPC-HDW5231R-ZE, since the IVS events of the IPC-HDW5442T-ZE do show up.
Just after the IVS events stop displaying on the NVR"s timeline; the 5231 logs show 'abort' log type and then a 'start up' followed by a 'save configuration' (content: name: Video Format).
The 5231's webinterface can be slow/sluggish as well.