Compost should not have that affect on things. Have you tested the soil in the containers? It could be off on it's Ph, or something else. How long have the herbs been in the containers? With the recent heat, could they be getting ready to bolt? Do you trim them back regularly?
I noticed today that most of my herbs in the bed farthest from the house are trying their hardest to set seed, I haven't been using them enough lately I guess.