Sorry for the late reply, i went back to 2.6.2 as it works without issues with all the models i tried. I have now downloaded the latest 3.1.0 and it still does this strange first layer when supports are enabled, I couldnt find the exact setting you mentioned, but i did find under general settings "Auto drop models to build plate", not sure if that worked. If i put the model to anything over -.1 it wont slice and greys the model as if its outside the build volume.