Magma cubes and slimes climb everything climbable and die because of entity cramming if we have 25+ of them because they are no longer inside a vine block. Any other mob stays at the bottom and cubes do climb.
To reproduce:
Build a 1x3 chamber with walls around it
Place any type of vines inside
spawn size 0 cube inside
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I'd like to mention that climbing ladders is expected behavior that has been resolved as Working As Intended (see MC-148545), slimes being the only mob capable of climbing vines though is unque and unexpected behavior.
Can confirm in 23w42a