Hi there, and thanks for letting me know. I'll take a look as soon as I can.
Out of interest, are you able to share your workbook (privately by email is fine if you don't want to attach here - d.s.marsh@gmail.com)? It'll be good to investigate your particular situation in context and to see the data you're working with. Either that or a link to the dataset (if publicly available) would be very useful.
Root cause:
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