I greatly apologize if this is a duplicate case, but after searching google with multiple matching keywords I found nothing.

Anyway- Today, I booted up my 2.5 year old world on MCBE, and immediately in the sky saw chunks of floating leaves that appeared to be trees. Alongside this, was a random water source block that had generated also in the sky. These have never appeared before.
THINGS TO NOTE: My speculation is that this is the game getting confused and inserting decorations from what my seed would be had it been organically 1.18 from the start.
(Went back and this was slightly confirmed- Loaded up the seed in a completely 1.17.4 world with C&C enabled, tped to the coords and was on a tree in a meadow biome. Do with this what you will, I guess.)

What I mean by that is, while I'm on 1.17.4, my base was loaded in older chunks and I had also switched to the experimental updates for that world.

About 2 days before this, I'd noticed something really weird going on with my world's file size- It had gone down. Randomly from 940 (megabytes), to 900, then to 960, 920, and now it's at 900. I'd left the world before reporting this bug and went back in to get screenshots, before finding that some of the previously existing leaf chunks just.. disappeared.

Another 2 things to note-

I am an avid user of Riptide III Trident + Elytra travel, which I can imagine would cause a lot of stress on the world with loading chunks. (this is a single player world.)

I also recently updated to Win11, though the issues only began happening a few days later.

Also, sorry for the low brightness of the pictures. Windows-XBox integration on my PC kinda just stopped for some reason, so Win+Alt+Prnt doesn't really work now. I had to open chat then use snipping tool.

Seed: -1684854720   Coords: 2112, 132, -2148  Specs: RTX 2060, 24 gb ram, Intel i7-9700k