So SkipTheTutorial made a video showing how you can use the 'Scale' attribute on the player to make better parkour, so I tried it. It was pretty fun, yet an eyesore to create, but at some point, when my character is at a custom scale, it just went back to normal. In some cases, you'd clip through floors and walls! This was kind of annoying, and basically drove me nuts
I did this in a WorldEdit modpack, but WorldEdit doesn't affect the command, so you can't say it's invalid. I was also in 1.21.1, but no future logs show that it's been fixed, so you can't say it for that reason either.
PLEASE FIX IT!!!!!!
How to do:
grab a command block and pressure plate
place the command block, place the pressure plate on top
write this command: attribute @p minecraft:generic.scale base set <# that's not 1>
step on the pressure plate
move around a lot. Note that this randomly happens.
watch it happen
7(BONUS). stand next to a wall and hit the W,A,S,or D key on your keyboard, depending on where you're facing and where you are, when you resize unexpectedly, and you might clip through the wall. change the wall into a slab, and same for the floor. do the same thing and you might also clip through the floor too.
It may take a few tries.
You have to test issues in vanilla for them to be accepted here. Mods tend to alter the game in unexpected ways. You must also verify it happens in the latest release or snapshot, not just old versions; lots of things get changed between versions that don't end up on changelogs (eg just small rewrites of code, that can cause or fix issues).
You're also missing steps to reproduce.