if you are placing markers in Wwise manually (or detected according to transients) on a source file that didn't have markers when you imported it, it works ONLY if you convert the source file after applying the markers.
It is also necessary that the relative event plays the Platform object only, NOT the original, otherwise it will just randomize the playback start position without seeking the marker.
If you import a file with markers already in, it will work straight away even if you play the Original in the Event.
You still need to convert it if you want to play the Platform Object only though.