Was doing the Glory of the Dragonflight Hero achievements in Azure Vault - Going for both the "You Must be Made of Hide" and "The Cracked Crystal" achievements on Umbrelskul. As soon as the encounter began I kept getting bug reports

1882x ...nstanceAchievementTracker/AchievementTrackerCore.lua:2611: attempt to call field 'track' (a nil value)
[string "@InstanceAchievementTracker/AchievementTrackerCore.lua"]:2611: in function `?'
[string "@InstanceAchievementTracker/AchievementTrackerCore.lua"]:176: in function <...nstanceAchievementTracker/AchievementTrackerCore.lua:175>

Locals:
Skipped (In Encounter)

Fixed for next release V4.40.0. Thanks