[2021] Levelling not working in Siege of Paris

I'm playing Siege of Paris, and am powel level 452 with 148 Mastery points.

All enemies I encounter in this DLC have been of red difficulty - even though the region power level is only 200. I have tried changing the Levelling, and had the following results:

Levelling off: All enemies came up as green (easy)
Default: All enemies came up as red (challenging)
Constant: All enemies came up as red (challenging)
Hard: All enemies came up as red skull (overwhelming)
Nightmarish: All enemies came up as red skull (overwhelming)

It seems that "normal" levelling is broken - its either far too easy due to levelling being disabled, or else set to a harder level.