I currently have a ticket open with Groups.io support on this, as the same behavior is not being displayed on any other Groups.io group to which I subscribe, and I changed at least half of them to "Individual Message" status this morning so that I'd get individual messages. To a one, they're all showing the groups.io standard link cluster fully and correctly after the phrase, "You receive all messages sent to this group."
I will report back on what I hear from Mark Fletcher (the owner and primary tech support for Groups.io) regarding this. It will probably be a few days, as this is not a critical issue.
Not the sort of thing I'd expect to be rearing its ugly head this long in to the history of Groups.io, but perhaps it's always been there and there's something distinctive about this group's custom footer content that's breaking it. That's up to Mark to flesh out.
Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
The psychology of adultery has been falsified by conventional morals, which assume, in monogamous countries, that attraction to one person cannot co-exist with a serious affection for another. Everybody knows that this is untrue. . .
~ Bertrand Russell