Wither skeletons do not to pathfind their way to players if they are below an opaque block. Wither skeletons are immune to burn in daylight, and they shouldn't be doing that. Any opaque block, including trees, will stop the wither skeleton from chansing you even if they are immune to fire or daylight. This is also an issue on Java. See MC-101136.

To Reproduce
1. Spawn wither skeleton in the Overworld
2. Go to survival and lure the wither skeleton to an opaque block
3. The wither skeleton will stop chasing you as theire is block above it.

Observed results
Wither skeletons don't chase players when they are under a tree as they think they can burn.

Expected results
The wither skeletons should always be chasing the player and not think that they can burn.