Stumbled upon this one last night, was able to recreate it.
Join a group successfully with group finder, get ported into the dungeon, leave by the door. When you return to open-world, get kicked from the group, you will still be 'looking for group' and unable to leave the looking for group que, longet we waited was 16 mins after leaving the dungeon. If you relog your char it removes you from the que.
This was on Xbox One X with a hardware restart between tests and saved local game data deleted between tests.
The Sacrificial Warriors GMXbox One EU:18x CP Chars (2300+ CP)Xbox One NA: 3x CP Chars (800+ CP)Xbox One (alt) EU:5x CP Chars (1500+ CP)Xbox One (alt 2) EU:1x CP Chars (450+ CP)PC EU: 1x CP Char (400+ CP)