Steps to reproduce:
- Start a rocket rush
- Buy 2 blue slim inserters and 2 chests
- Place chests next to each-other
- Try to make double blue inserter between them

image.png

https://prnt.sc/w_YHXaYtrZ-0
hmm, I cannot reproduce this

It is strange. I disabled all the mods just to be on a safe side and enabled only this mod + your library. Here is what I got: (using the latest available version)
` Error while running event Kux-SlimInserters::on_built_entity (ID 6) Unknown entity name: basic-slim-inserter_part-a stack traceback: [C]: in function 'create_entity' __Kux-SlimInserters__/events/on_built_entity.lua:105: in function 'on_built_slim_inserter' __Kux-SlimInserters__/events/on_built_entity.lua:58: in function <__Kux-SlimInserters__/events/on_built_entity.lua:43>
Could that be because I don't have SA while you got one?

Unknown entity name: basic-slim-inserter_part-a
that surprises me, it should actually be there.
I did test my mod only with the base mod. not buyed the SA.

did you disable "dual inserters" in settings?

Not sure about difference between double and dual so here are my settings

image.png

So yeah, probably need an extra check like

if game.prototypes.entity["basic-slim-inserter_part-a"] then
...
end

a "double" inserter is internally made by two insertes but build at once. both inserters have same setting.

a "dual" inserter is basical two inserter at the same tile. e.g. you can build a yellow inserter and additional a blue inserter at the same tile. both insertes work independently of each other. you can use diffent filters, you can fill both lanes with differnt items.