I'm getting a lot of these messages and it seems like its cause of the server lag.

[14:38:02] [Server thread/WARN] [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.
[14:38:02] [Server thread/WARN] [FML]: Doomlike Dungeons loaded a new chunk [60, -18] in dimension 0 (overworld) while populating chunk [61, -18], causing cascading worldgen lag.
[14:38:02] [Server thread/WARN] [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.
[14:38:02] [Server thread/WARN] [FML]: Doomlike Dungeons loaded a new chunk [59, -18] in dimension 0 (overworld) while populating chunk [60, -18], causing cascading worldgen lag.

If you are using 1.13 this is normal expected behavior; if it's 1.14 it's either a false alarm or something I can't find.

Try 1.14.8, the "cascading" world-gen is fixed in that.