Managed to figure it out and fix my game.
Looking at the code that others have posted for what worked for them, I noticed one thing: The hall of echoes waypoint ID was 29 above the crashsite ID. So it'd look something like this as a rough example:
<node id="Waypoints">
<children>
<node id="Waypoint">
<attribute id="WaypointName" value="WAYP_ARX_TheCrash" type="22" />
<attribute id="Region" value="ARX_Main" type="22" />
<attribute id="WaypointTrigger" value="0000000000" type="24" />
</node>
<node id="Waypoint">
<attribute id="WaypointName" value="WAYP_ARX_LadyVengeance" type="22" />
<attribute id="Region" value="ARX_Main" type="22" />
<attribute id="WaypointTrigger" value="0000000029" type="24" />
</node>
</children>
</node>
So if anyone else is having trouble with this issue, and the stuff posted in the steam thread didn't work out exactly, try taking the value of the Crash site waypoint and adding 29 in the XML. It should work.
