I repeatedly had this issue on the 'aloha.pk tower of babel' server, that i fall to death just by climbing up blocks (on the tower built by players). No matter how many times i try to reach that specific area, it always happens again at exactly the same place. This occurs usually during the game, not already from the beginning. The area was usually being heavily altered before (blocks added and destroyed).
My first guess was maybe some connection problems (my ping is usually around 200ms), but other players also mentioned it in the chat. I haven't checked another server, where the gameplay has lots of blocks added and destroyed, for this though.
Maybe related to this, in the same situation i also noticed that sometimes it is not possible to build by left-click, instead only drag & drop works.