Thanks, I already tried deactivating all plugins (I can try themes later, but each time I try this, it takes the entire live site down). Also, there is no HTTPS involved here – nothing is redirecting to SSL, I don’t even have SSL set up for this domain.
Also, this was written to WP’s error_log, without a date (only the first time):
ALTER TABLE wp_pmpro_membership_levels ADD INDEX ( enddate )
made by activate_plugin, include_once(‘/plugins/paid-memberships-pro/paid-memberships-pro.php’), pmpro_checkForUpgrades, pmpro_upgrade_1_2_3
I am admin, and I can’t dismiss it (it comes back on reload). Not pretty.