Pages resizing rows to fit height to content is greyed out

I had the same problem, too, and could not manually resize the height of the row because the "Fit" button for the row height was greyed out under Format > Table > Row & Column Size. My tables had a lot of text in them (not numeric tables). After playing around, I realized that this is not random, but only occurred for those rows which had text in one of the cells that ran right to the edge of the cell. It is as if Pages is inserting an invisible hard return after the last character even though visually the text fits the cell perfectly. To see if this is the case for your table, try deleting some of the text from the end (or even just a few characters) and see if Pages will "unlock" the Fit button and allow you to manually resize the row height correctly. Definitely a bug, but there seems to be a workaround if you are able to re-word your text and shorten it slightly so that the last character of text does not run right to the edge of the cell.