Since GVMP switched to rage:MP 1.1, everything works properly again. So: no use for the tool.
Get your Launcher config and change the "config.json" with values from "C:\Program Files (x86)\GVMP-Launcher\GVMP-Launcher.exe.Config"
If server restarts, just whitelist your self again, start the tool and use F1 -> Reconnect to reconnect.
If you want to reconnect while you're ingame, use F1 -> Reconnect & then start the tool.
Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.