In your log this is the problem:
[B#439] [08:23:12] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 8646ms behind, skipping 172 tick(s)
What happens is due to extreme lag - that's 8.6 seconds of lag there - the client is literally "skipping" or ignoring some of the information which it has been sent by the server. So the client misses the important information that the player is supposed to be inside a lander.
- The server thinks the player is inside a lander (so the player cannot break blocks).
- The client thinks the player is not inside a lander (so the player looks like he is outside, trying to break blocks).
(When you are playing SSP, "server" means the internal Minecraft server and "client" means the game you see on the screen.)
The lag is a known issue but I do not know the cause of the lag, we are still trying to figure it out. It could be caused by another mod. It could be just connected with lighting and rendering the asteroids on the client.
It is
not a world generation issue, the issue happens also when the world is already generated. (And we have some smart code I made which actually generates the world at the destination while the rocket is doing its pre-launch countdown.)