I have "Quest Giver Icons" in Settings turned on normally, but occasionally the quest markers (e.g. for the daily quests such as crafting writs) vanish, and I have to go back into Settings to turn "Quest Giver Icons" on again. It's random, unfortunately, and there's no point in me creating a video about it, because it's just something I observe on some days after logging in.

NOTE: this isn't related to update 38, I've seen this problem for months.