Trying to research the planet discovery but it says that I don't have the prerequisite researches even though I do.
I started on Vulcanus, so could it be due to a conflict with the Any planet start mod?

v2.6.3 ensures that there are no hidden prerequisites for Moon Discovery Cerys due to other mods.

Let me know if that fixes your problem.

Damn you're fast. Yep, that fixed it, thank you.

Same problem, latest everything. Overlapping? mods: Muluna, moon of Nauvis and Lignumis

I can provide the full mod list if needed.

I am using the Enable All Planets mod, a meta mod that adds all the space age planet mods

Modlist would help.

nvm

Modlist would help.

advanced_target_priorities_1.0.2.zip
Aircraft-space-age_2.3.2.zip
alien-biomes-graphics_0.7.0.zip
alternate-science-packs_1.0.1.zip
ArmouredBiters_1.2.1.zip
astroponics_1.6.2.zip
atan-air-scrubbing_0.2.5.zip
AutoDeconstruct_1.0.3.zip
Better-TrainHorn_1.0.3.zip
bioprocessing-tab_1.2.0.zip
cardinal_1.0.0.zip
cargo-ships-graphics_1.0.4.zip
cargo-ships_1.0.16.zip
castra_0.5.4.zip
Cerys-Moon-of-Fulgora_2.9.8.zip
cf-lib_0.0.12.zip
Cold_biters_2.0.9.zip
common-prototypes-graphics_0.0.1.zip
common-prototypes_0.0.1.zip
corrundum_1.0.36.zip
cubium_1.0.10.zip
DarkNight_2.0.0.zip
dea-dia-system_0.25.0.zip
DiscoScience_2.0.1.zip
doeworks-deer_0.3.0.zip
electric-trains_0.4.0.zip
electromechanical-combinators_20.0.0.zip
enhanced-shadows_1.0.2.zip
EpicArtillerySounds_2.0.1.zip
est-tiny-storage-tank_1.3.0.zip
ev-logistics_2.1.3.zip
even-distribution_2.0.2.zip
Factorio-Tiberium_2.0.11.zip
fdsl_0.1.9.zip
Flare Stack_3.0.6.zip
flib_0.16.2.zip
FluidMustFlow_1.4.2.zip
Fridge_0.2.1.zip
Gledub-Music_0.0.3.zip
gun_SnRif_f20_0.2.1.zip
hd_planets_2.0.10.zip
informatron_0.4.0.zip
InserterFuelLeech_1.0.0.zip
ion-thruster_1.2.5.zip
janus_1.2.0.zip
k2-anti-material-rifle_1.2.0.zip
Krastorio2Assets_2.0.0.zip
kry-all-planet-mods_1.0.11.zip
kry_stdlib_2.0.3.zip
laser_rifle_2.0.3.zip
laser_tanks_2.0.11.zip
lex-aircraft_1.2.2.zip
lignumis-assets_1.0.3.zip
lignumis_1.0.44.zip
LJD_Vehicles_Continued_1.2.3.zip
long_stack_inserter_1.0.1.zip
LouderCargoWagons_2.0.1.zip
LubricateCargoWagonDoors_1.0.1.zip
Manufacturer_1.1.0.zip
maraxsis_1.30.12.zip
metal-and-stars-graphics-2_0.0.3.zip
metal-and-stars-graphics_0.0.4.zip
metal-and-stars_0.1.10.zip
mf-buildings-graphics-1_1.0.6.zip
mf-buildings_1.0.7.zip
mf-core_1.0.3.zip
mf-logistics-graphics-1_1.0.0.zip
mf-logistics_1.0.1.zip
Milestones_1.4.4.zip
minimalist-rails_1.2.1.zip
mod-list.json
mod-settings.dat
mods.txt
Moshine-assets_0.3.14.zip
Moshine_1.0.15.zip
muluna-graphics_1.0.14.zip
muluna-utility-constants_1.0.1.zip
mushroom-cloud_1.0.2.zip
naufulglebunusilo_1.1.2.zip
Nuclear Fuel_1.2.5.zip
OverloadedTrains11_2.0.4.zip
Pi-C_lib_2.0.1.zip
planet-arrakis_0.4.1.zip
planet-muluna_1.38.3.zip
PlanetsLib_1.3.1.zip
playtime_1.1.1.zip
PLORD_Prometheus_GrenadeLauncher_0.3.6.zip
PlutoniumEnergy_1.7.13.zip
pollution-as-surface-property_1.0.1.zip
quality_glassware_0.1.0.zip
RealisticReactorGlow_1.200.7.zip
Redrawn-Space-Connections_1.3.10.zip
RITEG_1.3.10.zip
Robocharger-Updated_0.0.1.zip
Robot256Lib_2.0.10.zip
rotate-vehicles_0.0.8.zip
se-space-trains_1.0.6.zip
secretas_1.0.25.zip
slp-dyson-sphere-reworked_1.0.2.zip
snouz-big-accumulator_1.0.3.zip
snouz-big-solar-panel_1.0.4.zip
snouz_better_substation_1.2.0.zip
Soundpack-alerts-and-sirens-updated-v1-1_1.0.8.zip
SpidertronEnhancements_1.10.8.zip
SpidertronPatrols_2.6.2.zip
steamship-reloaded_1.2.0.zip
Superheating-Balanced_1.1.0.zip
tenebris-prime_1.3.2.zip
terrapalus_0.1.4.zip
textplates_0.7.2.zip
tile-upgrade-planner_20.0.1.zip
Todo-List_19.10.0.zip
Truck20_2.0.2.zip
TurbinePriority_2.0.0.zip
TurboBike_2.0.1.zip
uranium_geiger_0.5.1.zip
vanilla-loaders-hd_2.2.1.zip
vehicle-corpses_0.1.3.zip
vehicle-wagon-graphics_1.0.0.zip
VehicleWagon2_4.1.6.zip
vehicle_physics_2.0.3.zip
visible-planets_1.4.8.zip
vulcanus-sulfuric-bacteria_1.1.0.zip
Warehousing_1.0.3.zip
Water-Friendly-Walls_2.0.5.zip
wood-universe-assets_1.3.2.zip
Wood-Walls_1.3.1.zip
ZElectricVehicles_1.3.0.zip

Updated to latest everything - still no go. Maybe an option to manually trigger the fix-it code in settings, that re-enables the research?

The only possibility seems to be that another mod is running a final-fixes script that causes Cerys to acquire a hidden prerequisite.

It is possible for you to open up the prototype explorer to examine the prerequisites of Moon Discovery Cerys in your game. See what you can find there (and whether any mods are seen to modify that technology).

The mod Nuclear Fuel is the problem.
Enable Kovarex enrichment in the mod setting from Nuclear Fuel then simply research it in the game.