This may technically not be a bug, but I hope it’s not intended behavior:
When I open a portal before killing the boss, kill the boss, and THEN use that portal to go back, it is apparently still counted as “abandoned”. I lost progress and mods as if I had died/left early.
I noticed the portal is also blue, not green like it usually is when you create it after completion of the echo.
I’ve recently had resets without dying from time to time and read of other people having the same problem on reddit, it might simply be this unexpected/unintuitive behavior, at least it a was for me. (Playing poison lich. I sometimes just opened the portal while I wait for the boss to die.)