Playing galactic war in local server and "world simulation went away" happens a lot. Most occur in multi-planet system on late game, when the simulation performance went down below 50% and on some point all units freezed, after a while "world simulation went away" pops up. I 've install several mods include "Galactic War Overhaul","Bigger Galactic War","Shared Systems for Galactic War" and custom map packs.
Please open a new ticket at https://support.planetaryannihilation.com/ and include your logs there. Loss of world simulation usually indicates a loss of connection to the server.
Just realized you were on local server - Could be an issue with firewall or antivirus. I would start with https://planetaryannihilation.com/support/troubleshooting/
