Let G be the graph with edges 01 04 05 12 15 23 26 27 34 37 45 56 57 67, G' the result of contracting nodes 5,6,7 (and removing loops and multiple edges).

Choose an acyclic orientation uniformly at random in each of G and G'. Then P_G'[1->4] = 84/240 < 966/2706 = P_G[1->4], so contracting nodes makes it harder for 1 to reach 4 in this case.