Exact same issue. We have a few dozen clients and only ONE has a red dot but hovering shows the correct 'online + time stamp'. Needless to say, she cannot connect at all.
My fix the last 2 times (now happens once or twice a week) is to remove that device from that network, find it in unassigned (non-member) devices and re-assign it to her network. Instant green light. stinks because it requires her to be down, as for help, us to log in and do this quick fix, inform her to try again.
(Fully updated, Mac, no firewall, standard AT&T modem)