Using menu tokens (or similar?) to create "invite user link" on OG Group page
I was having similar trouble as you, due to the bug in menu-token.

The way I would go about is, as a work-around, is to create a views-block relative to your groups, adding your node id or gid as a field that is not displayed (you'll have to move this to the top of your fields list in views for it to work). 

Then you add a "global text" -field with a value like "Invite", re-writing the output as a link that includes the node id/gid as a token in the URL. This must be located below the node id/gid in the field order(!).

Finally, you will have to set your views filter to restrict the output to the page a user is currently on, this way the Node id/gid field will return only the correct value. Also set your pager to a single result as measure of ensuring only one value is passed through.

Hope this helped!