Hierarchy - Needs Calculation error symbol

[pvans267]

Good morning,

I am busy working my way through a Power Pivot course on Udemy and have just created my first Hierarchies. However, when I have done so, I see a yellow warning symbol stating that the Hierarchy "Needs Calculation".
Has anyone encountered this before? I can't appear to find anything on Google, the course Q&A or Microsoft identifying this issue. I should add that the Hierarchy does appear to work correctly regardless of this symbol when I create a Pivot Table.

Thanks for any help that can be offered.

Kind regards,
Paul