If you do /effect give @s speed infinite 254 and walk through cobwebs, a glitch will slow you down unless you are sneaking on slime blocks.
To reproduce
1. Place a floor of slime blocks beneath you
2. /effect give @s speed infinite 254
3. /fill ~ ~ ~ ~20 ~20 ~20 minecraft:cobweb
4. Try walking through the cobwebs.
5. Try sneaking through the cobwebs
Expected results
The walking through cobwebs should be much faster than sneaking.
Actual results
Sneaking is way faster.
Video Below (Recorded on Phone)
1st part is walking, 2nd part is sneaking
https://drive.google.com/file/d/1OSc3ZSwWOyccvbCIz3xmP8JilDS1IX19/view?usp=drive_link
I cannot reproduce this. Walking through cobwebs is a lot faster for me than sneaking through cobwebs, even with a speed effect of a very high level.