Hi!
I also ran into this issue several times, this happen in online mode for me, and there is nothing special to reproduce, just walk over the Purple Mandate quest map, teleport home 1 time at least to sell the trash, and after return sometimes there is no more turning back, which means no more "T" teleport home / left click on spell/skill to learn. Teleport gives a big red error that "You cant do this right here" or something similar ...and this is the moment when you knew you fu**ed up, the game still let you do the map or go into subminimaps around, but this will kill your session and end your quest, because once you are down, the entrance do nothing on click, the exit do nothing on click, "T" still gives the error, and you are also unable to learn spells / skills. And you have no other choice that leave the game to menu or os and get mad because your time is wasted again.
I dont know that if that moment when I realize the LOCK but I am still on the main quest map without going down to minimaps could I finish and left it or not.
Heres is a small capture of the situation (https://streamable.com/oabwt2), and I also reported this through the support form...