How to Repeat:
Set up at least a 3x3 area of upper slabs/stairs, break open the middle, and spawn a silverfish inside. Then, place an upper slab/staircase over them.

Expected Behavior:
Silverfish should be able to pathfind under slabs/stairs since they are 0.3 blocks tall, enough to fit under them without suffocating.

Observed Behavior:
Silverfish will spin around randomly, unable to pathfind out from under the slab/staircase. When outside, they will also always prioritize jumping on top, rather than crawling underneath.

Provided screenshot would be an example of how to repeat the behavior. If it was animated, you would see the silverfish spinning.