Quick answer: Run the behavior tree from the AI controller, assign the blackboard asset, and ensure the controller possesses the pawn so the tree drives it.

A behavior tree not running is usually an unstarted tree or missing blackboard. Here is how to fix it.

How to fix it

1. Run the tree from the controller

The AI controller must call RunBehaviorTree with the tree asset. If it never runs the tree (or runs a different one), the AI does nothing. Start it in the controller's possession logic.

2. Assign the blackboard

The behavior tree needs its blackboard initialized, and decorators and tasks read blackboard keys. A missing or wrong blackboard means conditions never evaluate and the tree stalls.

3. Possess the pawn

The AI controller must possess the pawn it is meant to drive. An unpossessed pawn, or a controller not assigned to it, means the running tree has nothing to control. Confirm possession on spawn.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unreal Engine error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

Most of the time the fix is small. Seeing the failure clearly is the part that actually costs you.