I tried flying up there and you can't even do it, I can't get above 318. I teleported like you suggested and stopped at 321. There is some sort of barrier they have placed, I'm pretty sure the world is supposed to go to 320 of building space.
Mine went from 24 to 12, 2 updates ago and then back to 24. The current update has limited it to 16. Getting very frustrating, I assume its to prevent us from making the game run too poorly. I get that, but as someone who wants to experience larger render distance of the mountains and isn't too picky about frame rate in single player games it would be nice if they let us choose. Perhaps what would work better would be if the default render distance is capped at the recommended limit, but there is an advanced graphics option setting which allows more adventurous players who aren't expecting perfect stability to turn it up, similar to java edition. My PC is capped at 56 chunks and its very jaring being capped to a lower max, even if I just want to see the view of what's ahead briefly. I'd love it if the devs added the option to let us just type in a render distance and test it, so they wouldn't choose our minimum or maximum. I'd really like to see the mountains at least 32 chunks on my phone, even if it lags a bit.
I noticed this happens when choosing superflat or old world types. Everything loads normally, but when you reload the world most chunks you had placed blocks in get completely deleted from existence, while the remaining chunks you placed blocks in are pushed further down into the void so only the top remains. (I assume this is the real issue, but it only appears to happen where there are hills in a chunk in old worlds, since the rest gets pushed below the build limit.)
Been happening on my Android Phone as well. The rain is endless, with the increased fog render distance limiter, sleeping does not clear it and like you said, mobs burned, the drowned stayed in the water during the day. Closing and relaunching the world fixed the problem for me.
Its been happening on my android phone as well. Every time I reload the world it changes the chunks it decides to randomly delete. I went down a cave and nearly fell off, due to the void glitch. I then left my world and re-opened it while I was near the chunk error, standing close to the edge. When I re-joined, it teleported me to the surface and when I went back below the surface the chunk I was standing in had now also been deleted. I tried interacting with the area in creative mode and you can actually place blocks in the area, it works like any empty space should, you can bridge over the error to other chunks.
I was playing creative and tried another glitch somebody else had posted here. Currently it won't let me fly above 318 there is a barrier, and as the reported bug said, if you teleport to 330 blocks height you fall to 321 and then hit an invisible floor. I assume you are experiencing the same glitch in survival.