@Purban said in Unable to save the game in offline mode:

To fix this, you need to find "/gamedata/lua.nx2". Create backup for safety and rename the file to "lua.zip", find and extract file "userInit.lua". Inside, find this line (should be near the top) "doscript '/lua/ui/globals/InternalSaveGame.lua'". Delete it or comment out, save the file and put back into lua.zip. Then rename it back to "lua.nx2". After doing this, saving and loading started to work again for me.

This does appear to have fixed the issue. Though it's worth being aware that this undoes the fix that caused the bug in the first place, and risks allowing code execution by exploting an overflow issue in the way the game handles save names.
Make sure you're using trusted mods if using this fix.