For autolooting:
If it from @autoloot command, you need to set on your conf/groups.conf
OR
If you accidentally change this to yes,
https://github.com/rathena/rathena/blob/645ff8591a101836be97a961c82e83b4d691e9eb/conf/battle/drops.conf#L11
Change it to no.
For PK mode:
check your conf/battle/misc.conf