This question seems to crop up quite frequently on the Discord, e.g. someone just reported killing "20" capitals with "95%" alpha core officers, and getting zero alpha core items out of the deal. Then I've heard from another mod dev that there's a hidden (in obsfucated code?) bit where core drops from farming Remnants has diminishing returns.
20 capitals with alpha cores, let's see... base 5% chance for an Alpha Core, times 4 for a capital ship, 20% chance each. 0.8^20 is around 0.01, so, 1% chance of zero core drops - certainly not impossible, but not very likely either.
As much as I love the paranoia (and I love it a lot), there aren't any hidden drop-reductions in core code.
Are the drop_prob_officer_alpha_core etc. values specified in settings.json and referenced in FleetEncounterContext actually used to calculate drops? Are there further modifiers on top of this?
It looks like you've found it; it's handled in FEC.lootWeapons(). As far as I'm aware/can remember, that's the only place, though there *might* be some code elsewhere.
EDIT: Also, could mods be having funny effects on the drops?
Certainly! From changing FEC, to changing these settings values, to filtering the loot via whatever listener lets you do that, to probably some other things I'm not thinking about.