That happens when all players already left from game by pressing quit button.
So there some logs:
1652.571 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod Wave Defense Unlimited caused a non-recoverable error.
Please report this error to the mod author.
Error while running event Wave_Defense_Unlimited::on_player_joined_game (ID 43)
Wave_Defense_Unlimited/wd-scenario.lua:1477: attempt to index a nil value
stack traceback:
Wave_Defense_Unlimited/wd-scenario.lua:1477: in function <Wave_Defense_Unlimited/wd-scenario.lua:1473>"
1652.571 Info ServerMultiplayerManager.cpp:740: updateTick(98021) changing state from(InGame) to(Failed)
1652.571 Quitting: multiplayer error.
And we found interesting fact that we have mod-turrets and vanila turrets. Bonuses from upgrades menu goes to all of them or not?