So, starting in version 2019 it seems like doublewall doesn't work correctly.
For example in 2018 and before you apply a 2" insulation doublewall on a 24x24 piece of rectangular duct and use the criteria to inside Dims & inside Skin and it keeps the inside dimensions to 24x24 and makes the outsize skin 28x28. Starting in 2019 all the way to 2021 it just downsizes the inner skin to 20x20 and leaves the outer skin 24x24.
Also, I'm not sure what version it broke tbh but hangers on doublewall seem to always go to the inner skin.
I'm thinking I need to start re-evaluating how we need to calculate doublewall going forward.