Quick answer: Unreal Mass Entity spawn producing entities without your expected tags? The Mass Entity Config Asset’s tag list determines the archetype — tags missing here are missing at spawn.

A Mass spawner places agents that should have FActiveTag, but queries for FActiveTag return zero. The Config Asset doesn’t list it.

Config Asset Tag Slot

Open the Mass Entity Config Asset. Add an FMassTagFragment subclass to the tag list. Every entity spawned via this config gets the tag.

Adding Tags Programmatically

EntityManager->AddTagToEntity(Entity, FMyTag::StaticStruct());

Add tags at runtime to change archetype mid-life. Triggers archetype move — significant cost for large numbers; do at low rate.

Tag-Driven Queries

FMassEntityQuery’s AddTagRequirement narrows by tag. Entities without the required tag are skipped — even if all other fragments match.

Composite Tags

Combine multiple tags for specific states (ActiveAndAlive, ActiveAndDying). Each combination is its own archetype — balance specificity vs proliferation.

Verifying

Spawned entities carry the expected tags. Mass Insights confirms the archetype includes them.

“Tags belong to the Config Asset. Add programmatically only for state changes.”

Audit Mass Config Assets via a checklist — new agent types are easy to ship with missing tags that quietly break processors.