Turned out the different servers had been attempting to use the same inputs occasionally. I scanned the wallets for transactions with negative amount of confirmations, compiled a list & send them and then zapped away the failed ones. Then I realized that because I had cloned the wallets at some point, a big portion of the resends were actually duplicate! Sent over 230 GIN. I won't be counting who was paid double here, of course compellingly honest people can step up, noticing that the same amount got paid twice
These kind of double spends can't happen anymore as I changed the code so that each server pays on schedule, evenly spaced each hour.
After I finally come up with the code for creating a full payout history for each user, complete with txids, this double payout could in principle be counted. But hitting miners with negative balances retroactively like that just annoys people and they can easily change addresses. I'll probably just skip the duplicate payments then, while compiling the history.