Why is StateTree triggering an "Array index out of bounds" exception?

Development Programming & Scripting C++
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1

I’m using two MassSpawners to spawn crowd characters like in City Sample, each with different StateTree assets. For some reason, when transitions are triggered, I get an exception on this line with error:

Array index out of bounds: 65533 from an array of size 5

It seems like the CurrentStatus.State.Index (aka Handle.Index) is 65533, which is the StateTreeHandle::FailedIndex. I set breakpoints everywhere that FailedIndex and I can’t figure out how it’s getting set to that. Anyone else run into this?

I’m on UE 5.0.3.

2

Turns out this is likely a bug in StateTree that is fixed after UE 5.0.3 but not yet in a released version of the engine. When I switched to using UE5 built from the ue5-main branch it fixes this issue.