Cannot change session

At the request of a client we are testing moving a site to Pantheon hosting. In the process we have discovered the needed use of this plugin for sessions. We have installed the plugin but seem to have issues. The site is displaying:

Warning: session_id(): Cannot change session id when session is active in /srv/bindings/6dd16a19c38743349337771a37985223/code/wp-content/plugins/wp-native-php-sessions/callbacks.php on line 34

From another post in the support section my understanding is that other plugins may be initializing the session before this plugin so a mu-plugin needs to be created. After doing this though the issue still persists.

Sessions are used for a couple different reasons on this site in connection with the eCommerce functionality and are required. Any help in either resolving this or helping us figure out if this site will even work on the Pantheon setup would be appreciated!

I can provide needed access information privately.