I'm sorry no expert has chimed in to help you...I guess no one knows the answer to your problem. I have always found Autumn fern to be indestructable. Perhaps you are being too kind to them. They thrive in full sun with little water...be a little meaner and make your soil more free draining and leaner. Good luck.

Too much lime leaching from the cement (containers and wall/sidewalk)?

Could it be that the sun has changed its position and now these are getting the full wrath of direct rays? Other than that, there is not much detail regarding what is going on other than brown leaves. When the entire plant looks burned, it is usually a result of something phytotoxic in result. Perhaps an herbicide spray used on the lawn may have drifted, but I believe sun damage is the culprit. The ferns at the edge doesn't seem to be affected.