Walking while inside vines, ladders, scaffolding, weeping vines, twisting vines and cave vines (or any block in the #climbable tag in general) is slower than normal walking.

How to reproduce:

1. Execute the following command:

   /fill ~ ~1 ~ ~ ~1 ~20 minecraft:scaffolding

2. Optionally, execute the following command:

   /effect give @s minecraft:speed infinite 9 true

3. Walk around and through the scaffolding.
   → You move slower in the scaffolding.

Expected result:

A player in a climbable block should move normally if moving horizontally.

Observed result:

A player in a climbable block moves slower than usual.