Current implementation of dashsink (gst-plugins-bad) does not work with Dash.js (DASH IF reference player). The reason is the use of self-inizializing segments in the current implementation.
Even if DASH standard allows self-inizializing segments, DASH-AVC/264 guidelines implemented in Dash.js does not allow it. Further details are here: Self-initializing segments · Issue #861 · Dash-Industry-Forum/dash.js · GitHub
I have already an initial patch that allows the dashsink to work with Dash.js, but I need to do some further adjustments before sharing it.