When a bounty target has been killed, the following is logged to the console on client side:
[Warning: Epic Loot] SENDING -> RPC_SlayBountyTarget: Greydwarf_Elite (target)
From what can be seen, on server side the procedure call never completes / goes to timeout.
Never got to this log (in Bounties.cs):
EpicLoot.Log($"Bounty Target Slain: bounty={bountyInfo.ID} monsterId={monsterID} ({(isAdd ? "add" : "main target")})");
(Yes, the bounty was in progress and mine).
IMPORTANT EDIT:
It appears bepinex was incorrectly installed on the server (really have to check that every file is present).
This issue is not related to the mod after all. Everything works now when no files are missing/misplaced.
Sorry for taking so long to post here, hope it helps.