Are you playing on the official vanilla game (downloaded from Minecraft.net)? Because I can say with absolute certainly that this is the result of a mod, such as "Treecapitator" or "Vein Miner", or a data pack, not vanilla behavior - no "bug" can ever possibly make a whole tree break when mining the bottom, and only when sneaking (note second item under features), which needs to be deliberately coded in, and it certainly wouldn't only affect certain users as everybody downloads the exact same game from a centralized location (if you are playing the official game, that is) and file corruption can't possibly cause this (the launcher also validates the checksums of every file every time you play, except for data files (options.txt, saves, data/resource packs) - the only other way this could happen is if you installed a data pack.
Good call on that.
This is what I was thinking too. Since no-one else is able to replicate it, I am assuming it must be some left over files from one of the mods I used. When I re-installed windows I never copied my %appdata% folder over to my new user profile so i'm not sure how the mod files would have migrated over. I downloaded the vanilla Minecraft installer from https://minecraft.net/. I haven't installed any other resource packs or data packs. I will try to vein mine some ore and see if that also is mined, if it does then this has to be a mod file remnant or something.
SOLVED. JUST FOUND OUT WHAT IS HAPPENING:
So I copied my world over from my last computer. Inside of the world folder is a folder called datapacks. The file treecapitator for version 1.13.2 is in there and I guess it works for version 1.16.1 since it is still working.
Awesome find. Looks like TheMasterCaver called it