Slitherine

All my Australian units have had their nationality flags changed from Australia to Great Britain. Now when they deploy, they consume Great Britain command points, not Australian ones anymore. This bug may be linked to my first time saving of a replay file. I overcame the issue by deleting my corrupted “End Deployment Save” and “Campaign Save”, and then loading my “End Turn Save” from the previous scenario.

This may be caused by the Aussies 'borrowing' British unit types. You can do this in the editor if a faction is missing certain unit types. Kind of like a Commonwealth lend-lease.
Official scenario or custom?

Your Forgotten Army 1941-42 custom campaign, Singapore scenario.
But the unit type is "Australian Infantry '41" and "Australian Engineers '41". They are units with a different name but sharing the Great Britain faction models that exists in official campaigns right?

Aha, this is an old campaign created at a time when there were no or few Australian unit types. So I used whatever British unit types were available. This campaign needs an update, but I do not currently have the spare time to do that.