Yes probably due to excessive moisture in July above all. I had swedes under mesh then and had to remove half of them which had turned to mush, but the remainder are fine and look wonderful now, having enjoyed some extra space. I suggest you remove all the bad ones and expect there are some good roots there, maybe you missed noticing them earlier as the outer leaves can stay looking healthy for some time after roots are perishing. As for parsnips, probably canker from lots of moist soil around them, you sould still have good roots after trimming. Sowing parsnips in early June can help this, on wet soils, for lower yileds of cleaner roots.