When removing any armor from a certain player this error always happens:

The mod SpillProof (0.0.4) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event SpillProof::on_player_armor_inventory_changed (ID 37)
Given value has to be larger than or equal to: 0
stack traceback:
        [C]: in function '__newindex'
        __SpillProof__/handlers/handlers.lua:47: in function 'on_inventory_shrink'
        __SpillProof__/handlers/handlers.lua:79: in function <__SpillProof__/handlers/handlers.lua:50>

I can't reproduce it in a new game yet.

There's probably some internal desync of state. I've got a new approach that's less ideal performance wise but ultimately leads to a more robust experience, but there are some compatibility issues that arise with jetpacks due to how they are implemented (I have reached out on earendel's discord about a possible change but have gotten 0 responses)