Yep, that is the culprit. Based on Low Ceiling Area reduction rules, all 100% of your area is reduced from the Measured Area, this is why your calculated area is zero.
Go to the Options > Project Preferences > Zone Dialog.
Change the values in the "Area reduction under low ceiling" area of the Dialog.
Can you post a screenshot of the current settings of this Dialog?
Also, are the 3D bodies of your Zones cut by some other element, maybe a Roof?
Can you select all your Zones and display only them in 3D, then post a screenshot of that, too? So I could see both the exact 3D geometry of those Zones and the Low Are Reduction rules affecting their Calculated Area calculation?
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