I have my camera set to record only when it detects motion. Reviewing events from the other day caused the client to crash every time I picked one particular event.
So, I dug the .mkv out of the server and played it in 'Media Player Classic' which worked.
Bit odd that it cuts off though with motion occurring right in the middle of the screen. I don't think it should have done that. That particular area is set to 'average' sensitivity.
I suspect the two are related. This particular camera is on a WiFi link and in viewing the logs both WiFi cameras 'bounced' their connections right about the same time. Seems like if that happens the server doesn't finish out the file properly.