I'm seeing the exact same thing, and I don't remember having this issue on a previous install of ReShade. Random "new" geometry is being added to the scene. It vanishes momentarily when switching between full-screen and windowed (I believe CEMU recreates the render surface) but reappears as soon as ReShade is loaded, even with no effects enabled.
Using ReShade 3.0.7, and Cemu 1.9.1 (BOTW is fully updated as well).
I noticed that it doesn't only 'add' (or screws up) world geometry, but additionally, it also 'magically' removes and then adds back some patches of grass as I rotate the camera around Link. Also, some grass can be seen floating in mid air sometimes, either close to me or far away along side unformed world geometry. In other words it screws things up real bad. Simply removing Reshade entirely fixed everything (I.E. it's not the game doing that). It seems to screw around with the emulation I guess.