Hello,
I had a chat with a MemberPress guy, he told me to tell you that they identified the JavaScript which is the source of the problem :

In case you want to reach out to the Newspaper developers about the Options page issue. This is the javascript in their theme that is causing the problem with the Options page: /wp-content/themes/Newspaper/js/td_wp_admin.min.js

if (“string” === typeof b[0]) {
var d = “#*$~&”;
this.each(function() {
var c, e = (c = a(this).data(“tooltipster-ns”)) ? a(this).data(c[0]) : null;
if (e) {
if (“function” === typeof e[b[0]])
c = e[b[0]](b[1], b[2]);
else
throw Error(‘Unknown method .tooltipster(“‘ + b[0] + ‘”)’);
if (c !== e)
return d = c,
!1
} else
throw Error(“You called Tooltipster’s \”” + b[0] + ‘” method on an uninitialized element’);
});
return “#*$~&” !== d ? d : this
}

Thanks for your help !