Update 1.2.13 bedrock states that it will fix witches not spawning in witch huts. No release date.
I have the issue as well. I created a new world in 1.2 Survival, after spending time to find a seed with a witch hut.
1 witch at start. Killed it. No witches since then, plenty of other mobs though after I replaced half slabs with full blocks (due to a potential bug with half slabs).
Switching back to Java version until this is fixed, no point building in Survival without a redstone source.
I added my vote. 🙂
Update 1.2.13 bedrock states that it will fix witches not spawning in witch huts. No release date.