Jeremy, when i'm testing recipes and get disappointing tenderness results similar to yours i subsequently double the time. I'm usually reluctant to change both time and temperature in a retest, although it might be useful to split a roast into 2 packages next time to discover which temperature you like best in 2 cooks.
Yes, there's not a lot more lost juices in extended cooks. At temperatures below 60C, which is as high as i ever cook beef, i haven't found much increase in fluids after about 16 hours. In roasts SV cooked over 65C there is a considerable increase in fluid loss and decreased tenderness.
Did you record the roast's internal temperature after the 20-minute roast? If the roast was relatively thin it might easily have been pushed up into the tougher temperature zone. Meat colour usually isn't a reliable determination of doneness.