Protected Content plugin, /protected-content/ notification page not showing

Hi!

When non-members hit my protected pages they are getting this error instead of the "/protected-content/" page specified in the "Membership Pages" page of the plugin settings:

Warning: Creating default object from empty value in /mysite.com/wp-content/plugins/protected-content/app/model/class-ms-model-pages.php on line 353

Warning: Cannot modify header information - headers already sent by (output started at /mysite.com/wp-content/plugins/protected-content/app/model/class-ms-model-pages.php:353) in /mysite.com/wp-includes/pluggable.php on line 1179

- Viewing the "Protected Content" page also results in a 404 error (http://pbrd.co/1vElm6L)

Notes:
- I have already tried updating the permalinks and re-installing the plugin.
- Previously, I noticed this issue (https://premium.wpmudev.org/forums/topic/protected-content-plugin-settings-cannot-change-membership-site-pages#post-782480) which I was able to workaround by entering the full URL to my protected content page (i.e., mysite.com/whatever-I-wanted-to-call-my-protected-content-page), but it appears that this workaround no longer works after the most recent update.

Please advise.