It is currently impossible for me to reroll one of my quests, even though I haven’t rerolled a quest today.
Is it the Knights of the Frozen Throne quest, since currently that one cannot be rerolled. If it’s not that one, you may have accidentally rerolled a quest today when and you didn’t see, or your server has not rolled to a new day yet, and you can’t reroll because of yesterday’s reroll.
Today meaning “this calendar day”, or “the last 24 hours”?