The renew or upgrade subscriptions buttons were not showing for me.
After finding a solution in this thread (https://premium.wpmudev.org/forums/topic/upgrade-renewal-buttons-not-displaying-and-auto-renew-versus-finite), I tried to select all members and change the gateway from Admin to Paypal Express.
When I hit submit, the following error appeared.
Warning: Invalid argument supplied for foreach() in /home4/[accountname]/public_html/wp-content/plugins/membership/membershipincludes/classes/membershipadmin.php on line 1364
Warning: Cannot modify header information - headers already sent by (output started at /home4/[accountname]/public_html/wp-content/plugins/membership/membershipincludes/classes/membershipadmin.php:1364) in /home4/oporto/public_html/wp-includes/pluggable.php on line 876