Swift sneak makes player sneaking faster than walking on slime blocks. This just happens to slime blocks, those blocks who can slows entity down like soul sands and honey block don't have this problem.

In fact, it is so obvious that you can simply feel it without any complex measuring.

Steps to reproduce:

1. Obtain and equip leggings enchanted with Swift Sneak III (or V):

   /give @s netherite_leggings[enchantments={swift_sneak:3}]
   /give @s netherite_leggings[enchantments={swift_sneak:5}]

1. Walk across a line of slime blocks
2. Sneak across a line of slime blocks
3. Compare the speeds of when you walk and sneak

Observed result:
You sneak faster than you walk on slime blocks.

Expected result:
You sneak slower than you walk on slime blocks.