Our kerbs got breathed on last night by a frost giant from an alien dimension. Or something. The oregano and marjoram have wilted and collapsed in a heap of blight, and the thyme is showing signs of same. The basil, parsley, and sage look alright. The chives seem a wee bit pale.
What happened? No clue. Light, nutrients, water all A-OK. No big swings of temperature. So, in the absence of data, I'm going with the alien frost giant. But I'm open to other suggestions.