When you're trying to go down the scaffolding, you can't with the new touch controls scheme in the latest beta/preview.
How to Reproduce
1. Place down a tower of scaffolding.
2. Climb up to the very top.
3. Try to climb down by pressing the sneak button.
You can't get down the scaffolding by pressing the sneak button.
You should be able to get down the scaffolding by holding down the sneak button.