Hi,
After some more investigation, this is because UBlueprints (and derived classes, like UAnimBlueprints) are not loaded outside the editor. They are deemed to be editor-only constructs and their generated classes should be used in cooked games rather than the UBlueprint itself.
For reference, loading is controlled by UBlueprint::NeedsLoadForClient() and UBlueprint::NeedsLoadForServer().
See [this question][1] for more details.