The /spreadplayers
command will spread entities on the structure void block. /spreadplayers
commands should not set players onto non solid blocks, such as liquid.
Steps to reproduce
Run the following command on a superflat with void preset
/fill 10 -61 6 6 -61 10 minecraft:structure_void
Run the spreadplayers command
/spreadplayers 8 8 0 2 false @p
Observe that you will spawn atop the structure void and fall.
Replace some of the structure void blocks with solid blocks and observe that you will still be placed above them even though there are possible blocks to spread to.
This also applies to grass and tall grass, which can actually lead to people falling into lava pits in combination with MC-610
Tested in 1.16.5