Additional info from the dev behind Full Stripe:
“The “Manage subscriptions” page uses templates to display its content.
The templates are encapsulated in script tags like this:
<script type=”text/template” id=”wpfs-subscription-cancel-success-message”>
Cancelled subscription.
</script>
I can see these templates in the HTML source code, but when the “Manage subscriptions” page is loaded, something removes the templates – most probably the javascript code of another plugin.”