This is definitely a bug.
Sometimes, it becomes impossible to assign values to actor array variables of actors placed in the world in the editor.Normally, values are assigned using the eyedropper tool or by selecting from a list, but when this bug occurs, “None” is forcibly selected regardless of which tool is used.
The exact cause is unknown, but my guess is that it occurs when new actors are placed in or deleted from the world.Restarting the editor didn’t fix the bug, and ultimately, it was necessary to delete the actor and rearrange it.
This is very annoying, so please fix it as soon as possible.