Hi Phil,
It’s a theme issue.

Please add the following css to Appearance->customize->Additional CSS

    @media screen and (max-width: 666px) {
        body #buddypress div.item-list-tabs#subnav {
            height: auto;
        }

        #buddypress div.item-list-tabs#subnav ul li {
            float: none !important;
        }
    }

The breakpoints is based on your theme.
After it, clear the cache and let me know if it works for you or not?

Regards
Brajesh

Thank you. Marking resolved.