I selected Burning Crusade as my Timewalking Campaign as a 47 alliance priest but I was sent to the Draenor expansion when I went through the dark portal.
Still an issue. I took the TBC campaign as my level 45 priest. Entered the dark portal and ended up at Warpath.
Works for me, you have to port there from honor hold npc that chromie tells you or you are sent tot he wrong dark portal. If khadgar and orcs are outside you did it wrong. It is a phased version of the dark portal with the time npc in blasted lands