CubedCraft is now supporting 1.13 to join with but we're recommending to still use 1.12 since 1.13 is a big laggy since the worlds are using old chunks format.
All connected blocks such as fences, double grass, etc, are not displaying correctly for 1.13 clients.
This is due to ViaVersion not functioning properly for 1.13 clients we hope to have it fixed tomorrow.
You must have ViaVersion installed on your server to be able to join with 1.13