The Better Together Update / 18.104.22.168 patch notes say:
"- Mobs will now avoid cacti, fire, and lava"
But they don't seem to avoid fire at all.
Avoiding lava seems to work perfectly for most mobs, except slimes. Slimes literally jump in lava.
How to reproduce:
- Put a very simple fire maze/wall around a villager or a zombie for example
- Most of the time they will just walk through the fire