The strange tree on the map remains after finishing the quest and Averon moving to the temple garden, and it won't let me pass to go to Larklast. It just brings up the options to get out of there (resets to the map with you still on the thesselia side) or visit the tree (which is now just a normal tree devoid of magic).
I tried with a new game as well as an old save file, with all other quest that I can complete, completed.
I play the browser version, on android.
(Really enjoying the game otherwise though and am looking forward to downloading when I get a laptop)