Have the same issue. Fresh install of the game. Everything on my system is updated. Win 10 1909 Home edition, on a laptop tablet pc. With an Intel HD Graphics 520.
Seeing this issue on Bedrock Windows 10. With all the slabs, especially. They're showing as grey. Which kinda sucks, cause I was trying to do some simple pixel art on my mob farm roof. Guess I'll have to wait, or use some other unspawnable blocks, till this issue is fixed.
@GoldenHelmet I've had the exact same thing as Rogue Cheddar happen in a peaceful world, with no hostel mobs, so it's definitely not a light issue. I have all my Villager locked up now, so they can't move around. Seems to help. But I had a horse tied on a leash, same thing happened in peaceful, horse disappeared, leaving the lead tied. I've had bees disappear to. Whole nests empty. Based on my experience with testing it. It's definitely got something to do with loaded chunks, and mobs coming in and out of those loaded chunks. Or with loading from a save or nether portal. Confined mobs rarely despawn.
I've lost so many villagers to this bug in my village, I've pretty much giving up messing with them now. This breaks so much in Minecraft. I run Win 10 and Android version, and have a realm. Between this and realms not loading, almost makes me just wanna quit. Cause it's not the game it should be, and hasn't been for ages. I tried naming them, locking them up, maxing them, etc. Still lose some occasionally. It's ridiculous. Between these bugs, and Win 10 update being so much fail, I seriously wonder about the quality of Microsoft's Programmers these days. These kinda bugs should be resolved in beta testing, we should literally never see this mess. Ya'll need to get your act together, or us paying customers gonna take our business elsewhere, for real. 🙄
I'm gonna add a tidbit of info that may or may not be helpful. As I already posted, I had this issue, but as of 2 days ago, I was able to upload my world on windows 10, before I could not. The only thing that changed, was a recent update to my wifi driver. Could be totally unrelated, as I dare not test it further atm, being it actually worked. Could be something Mojang did, the driver, or just a fluke.
The last update yesterday, fixed this issue for me, and yes, I had tried replacing them. It was a legit bug for some users, that they obviously just fixed, for me anyway. Hopefully the issues have been resolved, and this will close soon.