Zombified piglin, and wither skeletons do not like to pathfind through lava, or fire. Both of these mobs are fully immune to fire damage, and therefor should not have any issue with these things.

This was also a bug on java edition until 1.14~ and needs to be fixed on bedrock as well.

How to reproduce for fire:
1. Make a 2 wide line of fire around a 3x3 center area
2. Stand in the center of the 3x3, and spawn zombified piglins and withers on the outside of the fire.
3. Go into survival, and you will see them struggle to get past the fire, they will do it, but while they are standing in the fire, they will act like they are on fire (jumping around, spinning in circles, being dumb etc)

How to reproduce for lava:
1. Replace all fire with a 2 wide moat of lava.
2. Go into survival, and agro the mobs. Neither of them will want to jump into the lava, instead needing to be pushed in. Once they are in the lava, they won't move or pathfind at all.

Expected results:
For both fire and lava, neither mob should have issues walking or pathfinding past the thing that does no damage to them.

You can see footage of this bug here, along with direct comparisons the working java mechanics: https://youtu.be/CRwmy_XiGK0?t=435