Noticed this glitch a few times, with a few quests. Any of the repeatable quests seem to not work when trying to do them more than once. Once I do it once, it works just fine, but trying to do any of them a second time breaks it. It won't detect any new mobs killed, or tasks done, and I need to relog to fix it. I have never had it work, and always had to do it like this.
I would check in singleplayer, but the modpack I'm playing doesn't do so well with single player (gregtech new horizions).