Hey Tim,
I’ve seen users here that are running membership sites so this only is a matter of how you use a membership plugin. We have no record of what the plugins are though and because we haven’t performed an official membership plugin test, we can’t recommend any. I see you already posted a similar question in our Peer To Peer Forum. That is the correct forum for ask plugin recommendations because users do have more experience using third-party plugins.
Though we don’t have third-party plugins support, we like to know if our products do have issues. When you said shortcodes don’t work in X, did you test the shortcode inside the default WordPress editor and not Cornerstone? It is important that you specify so we’d know if there’s a problem with our products and where that problem is specifically. Please post your membership plugin’s shortcode in the default WordPress editor or Classic editor and check the frontend using X and then switch to the default WordPress theme or the Twenty Nineteen theme. That is because the membership plugin’s shortcode might not work in page builders like Cornerstone. Also, test without any third-party plugins.
Thanks.