17.01 09:34:50 [Server] Server thread/WARN [FML]: RFTools loaded a new chunk [-4, 35] in dimension -1 (the_nether) while populating chunk [-4, 36], causing cascading worldgen lag.
17.01 09:34:50 [Server] Server thread/WARN [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.
17.01 09:35:12 [Server] Server thread/INFO [railcraft]: Saving 269 Trains...
17.01 09:35:31 [Server] Server thread/WARN [FML]: RFTools loaded a new chunk [47, 4] in dimension -1 (the_nether) while populating chunk [48, 5], causing cascading worldgen lag.
17.01 09:35:31 [Server] Server thread/WARN [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.
17.01 09:35:31 [Server] Server thread/WARN [FML]: RFTools loaded a new chunk [47, 5] in dimension -1 (the_nether) while populating chunk [48, 6], causing cascading worldgen lag.
17.01 09:35:31 [Server] Server thread/WARN [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.

Probably not actually caused by RFTools. See if you can reproduce the problem with no other mods installed.

This issue has been marked as needing a response from the reporter for over 2 weeks without receiving one. As such, it has been automatically closed.