In Bluebeam Revu (Complete), subtotals in the markup list disappear when mixing different units.
E.g.: I've measured 10 lengths and subsequently I change 1 of the length units from meter to centimeter. You would expect that Revu can still add up 29,51 m + 72 cm = 30,23 m or 3023 cm but none of these values appear.
I can imagine it is unclear whether the subtotal should then show up in meter or centimeter. The unit of the majority of the markups is then preferred.