You may want to install DPKHelper or keeping monster kills records in any kind of way, because I farmed my Astra Bow just fine: I dropped some antennas before the drop rate change, some with the temporary method and what was left after they implemented the last one, I never went past 650-700 kills for a single drop and with the new system it’s THAT much easier to be honest.
So either someone stole your loot or you didn’t notice it dropping behind some huge trees since we still have this annyoing bug that doesn’t let us see our character behind map structures…