Intrusion Detection & Line Crossing event markers during playback on DS-7604NI-K1

I'm recording continuously with my DS-7604NI-K1 (2 cameras) and have intrusion detection & line crossing event notifications set up. It's all working OK apart from the event markers aren't showing during playback. When I initially tested motion detection, the markers showed under the blue line during playback, but now I'm using Intrusion/line crossing they don't show - I've tried selecting them from the LOV with the dotted square & bin symbol.

My cameras are:

DS-2CD2563G0-IS...

Intrusion Detection & Line Crossing event markers during playback on DS-7604NI-K1