Roger de Clifford, 2nd Baron Clifford - Either his descendants dates are off or the line is off.

You have Robert De Clifford being born 21 Jan 1299, his daughter Christian in 1320, her son Thomas in 1272, his son Thomas in 1303 (who is the husband of Catherine who in Christian's sister., and his son Thomas in 1330. If you put it in a chart starting with Thomas, 1330 it appears that Rogers daughter married his Great Grand Son.