I have a tendency to not dry enough.
Sometimes, the last quarter gets moist and difficult (even if dried well).
As I tamp and relight, it eventually gets more challenging to relight.
When that happens, I'll gently poke the ash layer to loosen and dump the ash. Then I'll stir, pry and loosen the unburned material. After it's "fluffed up" a bit, let it sit for 10 or 15 minutes, then it usually relights easier.
I think getting most of the ash out before letting it rest aids in keeping the flavor nice.
Otherwise, dump it. Life's too short to fret over the nickle's worth of nasty leftovers. I have to remind myself of this occasionally. #firstworldproblems