This came up recently and the players pretty much kinda had a revolt against me on it claiming that no matter how many fatigue/stress symbols appear on the reckless dice roll, it only generates one fatigue or stress, and not one for each icon rolled.
The wording on the icon's description is somewhat vague as it just says that if at least one of the symbols shows up in the roll, but it doesn't specify you gain one token for each icon rolled.