Excel gets extremely slow adding formulas

I've got lots of sheets with complex formulas, many tabs large, many columns and rows long.
But this one has me stumped. I've dropped the data into 6 tabs (Jul - Dec) and I built and tested the formula (July tab, starts at H2). I'm happy with it. And only about 100+ rows per tab. But when I go to copy the formulas down the columns, the whole thing turns into molasses in Alaska in winter. I have much more complex formulas behaving nicely in other sheets -

I would appreciate any insights
thanks

file attached (sort/subtotal macros kept on external sheet and currently disabled)
names in files, and uncalculated production values, nothing 'personal'