Hidden Vaal Pathways does not guarantee a Vaal side area

While doing No Stone Unturned achievement I've encountered an issue where the prophecy would not activate despite me being in an area where it should be, travelling to other areas did not activate the prophecy either. I have always traveled to a new area (through Ctrl).
Prophecy did activate after I have sealed and activated it again(sometimes I had to re-seal it several times).