C and G are not working

I assume you have check first common mecanical or key mapping issues ?

You have an english/us keybord (querty) or another type ? Some multiplayer server remap keys for other uses, and that can be an issue if you have a rare type of keybord.

If it's only happening in multiplayer, it indicates that the server maybe uses a plugin which suppresses this key input Input handling in singleplayer and multiplayer is identical, so if the game properly recognizes the input in singleplayer, it's unlikely that there is a technical issue. Maybe try to join a different multiplayer server (for testing purposes) and see if the key input works properly there