I tried to upvote your parent comment earlier today but the action did nothing. Your karma did not increase. I was able to upvote it just now, though it's stil

I tried to upvote your parent comment earlier today but the action did nothing. Your karma did not increase. I was able to upvote it just now, though it's still in the gray. I have noticed that a minority of comments seem to be "locked" against voting for a certain period of time. I have previously found unvotable comments like yours, spotted them again hours later, and found that voting worked again. I haven't been able to spot any common patterns in these temporarily unvotable comments. I wonder if there is some sort of cooldown timer on voting for comments that have received heavy voting in both directions. I'm not entirely satisfied with that guess, because IIRC some unvotable comments I have encountered in the past appear to be anodyne and unlikely to have attracted prior vote controversy. There's also a limit on how frequently your votes will affect another user, but I hadn't voted on any of your other comments in the past day.