The seasonal challenge to kill 5 Choristers before they finish singing has been stuck on 2/5 for me ever since the week that challenge came out. Is this a bug? Has anyone else had an issue with it getting stuck? I've been Thundercrashing into it/unloading rockets and nuking them as soon as they spawn in, so I'm definitely killing them in time. They barely have time to move from the spot they spawn. If you've managed to get this challenge "unstuck", what did you do?