My roommate who I play Minecraft Xbox One Bedrock Edition Beta split screen with and they can't unlock Renewable Energy, even though we did it all right, and they can unlock the other achievements just fine. We are currently Achievement Hunting and that one is not unlocking even though it was done roughly 5 times and we saved and quit and rejoined and tried again and still nothing.
So I commented on a similar thing, and doing so here to for better visibility. Me and my roommate are playing Minecraft Xbox One Bedrock Edition Beta, and while achievement hunting, we finished the Plethora of cats just recently, and I was helping them with getting the renewable energy. After they used charcoal to smelt wood into more charcoal, the achievement never showed up as complete, so we waited about 1-2 hours, then we saved and quit tried again, but when we logged back on, our 25 cats, our fox (which was gone before due to same issue), and our donkey (at least) were all vanished and gone from the game. We still have our Iron Golem that we made along with completing the Plethora of Cats Achievement, but everything else is missing (animal wise). I've been to the nether last time I played (when I got the fox and the fox never Despawned when we both were in the Nether and came back. Nothing happened on that front.) So the Nether DIDN'T CAUSE MY ANIMALS TO DESPAWN!
So I'm having a similar issue as Kieran Hughes. Unlike in MCPE-21416, I have not gone to the nether in this session. I play on the Xbox One Bedrock Edition Beta. Me and my roommate have been working on getting achievements. We had just completed the Plethora of Cats achievement and I was helping them with getting the renewable energy achievement, we finished that, but it wasn't registering so we saved and exited the game, when we got back, all our 25 cats were gone. We have also lost a fox I brought back due to this issue, and we lost at least one donkey. Prior to this, going to the nether and back DID NOT cause the animals to despawn. If you comment saying that this is associated with the MCPE-21416 than I will make sure to have it all recorded next time so you can all see that it is different.
I have that on singleplayer 1.8!
That is the current version we are playing on.