Having a similar problem using iOS on iPad Pro. Since 1.16.101, when I try to play my world that I’ve been playing for the last few years, the “Generating World” screen lasts for 5 minutes or more before the world loads. (It feels like I’m now playing on an old Commodore 64.)
When the world finally loads, it’s as though Minecraft time had passed during loading— if I had saved the game during daytime, it’s now nighttime or sometimes I die immediately.
Having a similar problem using iOS on iPad Pro. Since 1.16.101, when I try to play worlds that I’ve been playing for the last few years, the “Generating world” screen lasts for 5 minutes or more before the world loads. It continues to scroll the usual messages and tips (number of fish types, not killing dolphins, etc.). This happens for 640 MB survival worlds and 5 MB creative mode worlds.
When the world finally loads, it’s as though Minecraft game time had passed during loading— if I had saved the game during daytime, it’s now nighttime, or vice versa. Or sometimes I die immediately from a monster attack.