PMPro incompatible with Pantheon

The following steps will result in making the admin panel inaccessible. I have repeated this 3 times with same results just to test.

1. Set up a new WP site on Pantheon & login.
2. Install PMPro plugin
3. Attempt to activate the plugin. An error occurs:

Warning: session_start(): user session functions not defined in /srv/bindings/e399587393c84985b6bf6366fa406a0d/code/wp-content/plugins/paid-memberships-pro/paid-memberships-pro.php on line 27 Fatal error: session_start(): Failed to initialize storage module: user (path: ) in /srv/bindings/e399587393c84985b6bf6366fa406a0d/code/wp-content/plugins/paid-memberships-pro/paid-memberships-pro.php on line 27

For reference, line 27 is a call to session_start()

Pantheon takes issue with this session_start() and recommends installation of their Pantheon Sessions plugin (https://wordpress.org/plugins/wp-native-php-sessions/).
4. Install Pantheon Sessions plugin and activate.

Now… 

Refresh admin panel and you consistently get:

This webpage has a redirect loop
ERR_TOO_MANY_REDIRECTS

You can access the front end, but not the admin panel. Pantheon is unable to provide support since the issue relates to PMPro’s use of sessions, they report.

My site is completely unusable now.

https://wordpress.org/plugins/paid-memberships-pro/