So last night I went after the 4 hunters who spawn at the Christmas tree. I killed 3 but the 4th one killed me, but I have all 8 ivory keys. I tried to summon them again on multiple following night cycles, but the option for the lever never appears. I am only missing the Phantom mask, which happens to be the one I want the most, go figure. Is it intended to not be able to resummon the hunters after you have all 8 keys? I feel like it wouldn't be.