This isn’t frost damage on these plants. First of all, daffodils can tolerate spring frosts as you have seen in the past. Secondly, if it was frost damage you’d see the same browning on more plants, not just that clump. Or you do see it on other groups that aren’t in this photo? If so, frost is possible but I’d still say unlikely. We’d recommend that you dig up the worst of group shown and look at the bulbs/roots. One possibility is that something has eaten the roots or part of the bulbs – the plants could have had enough energy in what was left of the bulbs to break dormancy and start to flower, only to have it all crash when they didn’t have roots to support that growth/flowering. If the bulbs look fine replant them. The second possibility is that something hit this clump. Dog urine, or something else. Also, was the lawn recently treated or fertilized? this could be fertilizer burn from lawn fertilizer being kicked and/or washed into the bed, possibly along with weed killer that is in some lawn fertilizers. If there are others that look this way and they too are near the lawn I’d suspect some lawn product as a cause. Since the bulbs won’t have the foliage to feed them for this year they might be gone – you could think about marking the places where the plants have died and replanting some bulbs next fall.