Date & Time: At least since 6.1 release (first seen 3-4 weeks ago, last tested 6/7/22 11:30 PM PDT)
Frequency: Always
World name: All (last tested Hyperion)
Character name: Onyxium Asurai
Monster name: Multiple (Ashdrake, Mud Biast, Comet Chaser, Surf Eft, etc.)
Class/Level: Any (capped or uncapped)
Party or solo: Both
Area and coordinates: Brayflox's Longstop (10.3, 6.5)

Steps:
1. Sleep monsters prior to fighting Aiatar in final battleground of Brayflox's Longstop OR leave other party members or Trusts fighting while pulling the boss
2. Wait 15 seconds for battleground to "seal off"
3. When party members/trusts teleport into battlefield, both the monsters and Trust NPCs are able to freely pass through the sealed gate (no collision detection)

Note this does not effect player characters - collision works fine for us.

This seems to be the only fight and only dungeon where this occurs. Not sure if it happened prior to the 6.1 changes to the dungeon.