I hear that census returns from the Portlethen area are “significantly” behind where what was expected.

Overall Aberdeenshire is where the census team would expect so far. There is still time to complete it; just answer as if it were 20 March.

There is more here: https://www.scotlandscensus.gov.uk/taking-part-in-the-2022-census/scotland-s-census-2022/