This bug has happened more than once and I have noticed it has so far only been after completing a Beacon echo, or the Orobyss fight to gain corruption.
The bug is that on the reward island after completing these objectives (with the merchant and stash), clicking on the Monolith stone opens a different Timeline web than the one I’m currently in.
e.g. currently in Ending the Storm, complete a Beacon echo (also happened with Shade of Orobyss fight), click monolith stone to choose next echo - it opens the Fall of the Outcasts echo web. Then I need to port to the main Ending the Storm island to continue in that one.
I appear to have left my Fall of the Outcasts timeline with 7 corruption in it and not completed the quest echoes, unsure if that is part of the bug’s cause. I may try to complete the quests again to see if the bug stops happening after.
** Update: I completed the Fall of the Outcasts quests again, and now I reached another beacon in Ending the Storm, and the bug happened again.