RE: Slicer is slicing my model horizontally for no apparent reason on MK4s
Thats usually an indication that there are model errors. You haven't shown the full screen or attached a project file but does the model in the tree list have a small yellow triangle next to it by any chance ? You might want to hover over it and see what the pop up says.
Although if you closely examine your second picture you will see some edges in a different colour, those represent no manifold edges so I'm 100% certain your model is broken and is non manifold.
Fix the model and it will slice properly. If you are on Windows you can use the right click and Fix through windows option. Doesnt always work but its pretty good.
For further advice you will need to attach at a minimum your model but preferably a saved Prusa Slicer project file.
RE: Slicer is slicing my model horizontally for no apparent reason on MK4s
OK thanks for the answer. It was exactly the problem, repairing the model inside Prusa solved it.