I've been awarded a silver badge (Necromancer) but the badge is not shown on my profile; is this a bug?
I also cannot see that badge in your profile, and you don't appear in the list of Necromancer winners. How do you know it was awarded to you? Did you get a notification bar at the top of MSO?
Sometimes it takes a few hours or even days for the system to award an earned badge. Normally, I'd say that if you were tracking the criteria (Answered a question more than 60 days later with score of 5 or more.) manually, you might just need to wait a bit.
In your case, though, I'm not sure you've met the criteria. (I'm also not sure you haven't.) I only see one answer for you, posted Feb 23 for a question asked Dec 4. That's >60 days, so the first criterion is met. Its score is 3 (+5/-2). It's possible that its net score was 5 at one point, but if it was downvoted to below 5 before the Necromancer award script was run, you wouldn't get the badge.