It seems like that was the issue, though I don't know why.

I fixed it by going into FAF settings and ticking Vault Fallback Location.

Rebooting my PC, updating FAF to latest, updating graphics drivers, updating Java and reinstalling FAF (though not redownloading everything) - none of this worked.

This happened both before & after updating to FAF 1.2.1. I'll try fix it and update this thread if I find a solution.

Here's the error report:

Unhandled exception:

state->m_rootState == m_state

Program : C:\ProgramData\FAForever\bin\ForgedAlliance.exe
Cmd line arguments : /init init.lua /nobugreport /log C:\ProgramData\FAForever\logs\game_12755532.log /gpgnet 127.0.0.1:36954 /mean 1238.53 /deviation 158.744 /savereplay gpgnet://127.0.0.1:55593/12755532/AntagonistBob.SCFAreplay /country JP /numgames 51

Callstack:
Unknown symbol (address 0x008d462c)

Last 100 lines of log...

warning: [C]: in function pcall' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import' warning: ...\faforever\gamedata\lua.nx2\lua\ui\game\gamemain.lua(997): in main chunk warning: [C]: in function doscript'
warning: [C]: in function pcall' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import' warning: ...r forged alliance\gamedata\lua.scd\lua\ui\uimain.lua(85): in function <...r forged alliance\gamedata\lua.scd\lua\ui\uimain.lua:83> warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): Error importing '/mods/common/units.lua' warning: stack traceback: warning: [C]: in function error'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import'
warning: ...\faforever\gamedata\lua.nx2\lua\ui\game\gamemain.lua(997): in main chunk
warning: [C]: in function doscript' warning: [C]: in function pcall'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import'
warning: ...r forged alliance\gamedata\lua.scd\lua\ui\uimain.lua(85): in function <...r forged alliance\gamedata\lua.scd\lua\ui\uimain.lua:83>
warning: Error running '/lua/ui/uimain.lua:StartGameUI': ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): Error importing '/lua/ui/game/gamemain.lua'
stack traceback:
[C]: in function error' ...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function import'
...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import' ...r forged alliance\gamedata\lua.scd\lua\ui\uimain.lua(85): in function <...r forged alliance\gamedata\lua.scd\lua\ui\uimain.lua:83> debug: Loading module '\000/lua/usercamera.lua\000' debug: Loading module '\000/lua/ui/game/missiontext.lua\000' debug: Loading module '\000/lua/ui/game/gamemain.lua\000' info: Hooked /lua/ui/game/gamemain.lua with /mods/supremescoreboard/hook/lua/ui/game/gamemain.lua info: Hooked /lua/ui/game/gamemain.lua with /mods/em/hook/lua/ui/game/gamemain.lua debug: Loading module '\000/mods/common/units.lua\000' warning: Unable to find file /mods/common/units.lua warning: stack traceback: warning: [C]: in function doscript'
warning: [C]: in function pcall' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import' warning: ...\faforever\gamedata\lua.nx2\lua\ui\game\gamemain.lua(997): in main chunk warning: [C]: in function doscript'
warning: [C]: in function pcall' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import' warning: ...forever\gamedata\lua.nx2\lua\ui\game\missiontext.lua(16): in main chunk warning: [C]: in function doscript'
warning: [C]: in function pcall' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import'
warning: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(154): in function <...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua:116>
warning: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(399): in function OnSync' warning: [string "OnSync()"](1): in main chunk warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): Error importing '/mods/common/units.lua' warning: stack traceback: warning: [C]: in function error'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import'
warning: ...\faforever\gamedata\lua.nx2\lua\ui\game\gamemain.lua(997): in main chunk
warning: [C]: in function doscript' warning: [C]: in function pcall'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import'
warning: ...forever\gamedata\lua.nx2\lua\ui\game\missiontext.lua(16): in main chunk
warning: [C]: in function doscript' warning: [C]: in function pcall'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import' warning: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(154): in function <...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua:116> warning: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(399): in function OnSync'
warning: string "OnSync()": in main chunk
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): Error importing '/lua/ui/game/gamemain.lua'
warning: stack traceback:
warning: [C]: in function error' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function import'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import' warning: ...forever\gamedata\lua.nx2\lua\ui\game\missiontext.lua(16): in main chunk warning: [C]: in function doscript'
warning: [C]: in function pcall' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import'
warning: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(154): in function <...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua:116>
warning: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(399): in function OnSync' warning: [string "OnSync()"](1): in main chunk warning: Error running lua command: ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(154): Error importing '/lua/ui/game/missiontext.lua' stack traceback: [C]: in function error'
...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function import' ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(154): in function <...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua:116> ...gramdata\faforever\gamedata\lua.nx2\lua\usersync.lua(399): in function OnSync'
string "OnSync()": in main chunk
debug: Loading module '\000/lua/ui/game/gamemain.lua\000'
info: Hooked /lua/ui/game/gamemain.lua with /mods/supremescoreboard/hook/lua/ui/game/gamemain.lua
info: Hooked /lua/ui/game/gamemain.lua with /mods/em/hook/lua/ui/game/gamemain.lua
debug: Loading module '\000/mods/common/units.lua\000'
warning: Unable to find file /mods/common/units.lua
warning: stack traceback:
warning: [C]: in function doscript' warning: [C]: in function pcall'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import'
warning: ...\faforever\gamedata\lua.nx2\lua\ui\game\gamemain.lua(997): in main chunk
warning: [C]: in function doscript' warning: [C]: in function pcall'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): Error importing '/mods/common/units.lua' warning: stack traceback: warning: [C]: in function error'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function import' warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(37): in function import'
warning: ...\faforever\gamedata\lua.nx2\lua\ui\game\gamemain.lua(997): in main chunk
warning: [C]: in function doscript' warning: [C]: in function pcall'
warning: ...alliance\gamedata\mohodata.scd\lua\system\import.lua(48): in function import' warning: Error importing /lua/ui/game/gamemain.lua: Error importing '/lua/ui/game/gamemain.lua' stack traceback: [C]: in function error'
...alliance\gamedata\mohodata.scd\lua\system\import.lua(52): in function `import'
warning: Error running '/lua/ui/game/gamemain.lua:OnBeat': attempt to index a nil value
stack traceback: