I wonder if the CLTV is not deployed in testnet yet
It could well be that not enough of the testnet peers have upgraded - I think the next step is to play with -regtest rather than -testnet (so you are mining your own blocks).
That's why I quitted using testnet (and people do not stop asking me why I do the tests in mainnet).
I emailed Josh Cincinnati from blockcypher.com and he said it would be better to run the test in our own testnet, or we can also use their testnet.
https://medium.com/blockcypher-blog/testnet-is-not-for-testing-5afa78b1394