Possible Bug - Lumber Mill (Pelagos recipe) requires "Assembling Machine I", but this item doesn't appear in the tech tree. The closest item is Electric Assembly Machine

just checked it
this item is not present in recipe if you have only ships of fools installed

if recipe is modified it's caused by some other mod.
Do you have other mods that modify this recipe?

If you do. I need to know which combination of mods cause this to happen in order to fix it

I can confirm. I have only Ships of Fools and its deps installed, the lumber mill's copper-based recipe does call for an Assembling Machine I.

Active mod list:

base v2.0.73
barreling-group2 v0.5.1
bplib v1.1.6
canal-excavator-graphics v1.5.0
cargo-ships-graphics v1.0.5
cf-lib v1.4.0
elevated-rails v2.0.73
EvenDistributionLite v1.4.5
Flare Stack v4.1.0
flib v0.16.5
FluidMustFlow v1.4.4
InserterFuelLeech v1.0.2
light-overhaul v0.2.2
lignumis-assets v1.5.1
long_range_delivery_drones_talandar_fork v2.1.1
lubrication_tower v0.2.3
mferrari_graphics_pack_1 v0.0.1
module-inserter v1.0.4
offshore_pump_require_power v0.1.0
pirateship v0.0.4
pollution-as-surface-property v1.0.3
quality v2.0.73
space-spidertron v2.0.2
SpidertronEnhancements v1.10.8
toshtaru-tank-flamethrower-reworked v1.0.9
water_spitters v0.2.0
Wood-Walls v1.3.1
wooden_platform v0.3.0
autofuel v1.2.2
cargo-ships v1.0.31
space-age v2.0.73
zzz-nonstandard-beacons v1.4.1
any-planet-start v1.1.28
AquiloTrenches v1.1.0
behemoth-enemies v0.0.8
bioprocessing-tab v1.4.1
boompuff-agriculture v1.1.0
burner_foundry v0.2.0
canal-excavator v1.13.3
colorful_biochamber v1.1.4
condensing-agricultural-tower v1.1.1
dynamic_platform_lighting v0.3.0
Electric_flying_enemies v0.1.9
FusionPoweredRobots v1.0.6
heavy_gun_turret v0.1.0
hungry_biolab v0.1.0
multi_surface_promethium_plate_recipe v0.6.1
PlanetsLib v1.17.0
skewer_planet_vesta_assets v1.0.11
skewer_planet_vesta_assets_2 v1.0.3
SpidertronPatrols v2.6.3
talandar_cargo_ships_tweaks v0.4.0
TFMG-platform-docking v0.2.1
true_ending_is_shattered_planet v0.2.0
tungsten_mining_require_lube v0.1.0
lignumis v1.5.1
maraxsis v1.31.6
skewer_planet_vesta v2.1.13
spoiled_trenches_of_fulgora v0.3.1
visible-planets v1.7.1
Cerys-Moon-of-Fulgora v4.21.4
diesel_engine v0.5.0
fusion_machines v0.2.0
lignumis_tweaks_delaying_inevitable v0.4.2
planetaris-arig v1.1.17
advanced_oil_rig v0.1.0
cargo_crates v0.8.2
diesel_cargo_ships v0.2.0
diesel_machines v0.2.0
lighthouse_radar v0.1.2
local-parts-production v0.1.0
nuclear_science_pack v0.7.2
rocket_fuel_is_now_fluid v0.1.3
sand_seas_of_arig v0.2.0
barreling_machines v0.1.2
depths_of_nauvis v0.9.1
pelagos v0.53.0
carbonut_agriculture v0.3.1
fishing-dock v0.1.9
molten_plastic v1.0.32
space_tree_agriculture v0.1.1
ships_of_fools v0.12.0

I might have idea what's going on. Try 0.12.1 and let me know if it worked

Recipe now no longer has the Assembling Machine - although that does make it differ from the gold-based recipe which takes 2 Burner Assemblers.