Comment 1 for bug 1739406

So at a guess you have a few 3rd party plugins installed that are *NOT* delivered as part of Terminator. One of these is more than likely still trying to operate using gtk2 style imports. Find it and disable it and the menu will probably start working again. As the message says, look for imports referencing gobject, instead of GObject. Of course, even better would be to check for an update from the original dev, and if one doesn't exist, perhaps even provide a fix to them. Note that simply changing the import is unlikely to work on it's own. The code will very likely need other changes.