Can't restore Managed Backup

When trying to restore Managed Backup from inside the plugin, checks go fine but then it returns "error" (not telling what".

In browser console there 500 internal error on admin-ajax.php call at this moment. In Managed Backup log there's "Unable to extract manifest" error.

The debug log gives: "[07-May-2017 19:16:56 UTC] PHP Fatal error: Uncaught Error: in /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-content/plugins/snapshot/lib/Snapshot/Helper/Restore.php:306
Stack trace:
#0 /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-content/plugins/snapshot/lib/Snapshot/Helper/Restore.php(20): Snapshot_Helper_Restore->_spawn_queues()
#1 /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-content/plugins/snapshot/lib/Snapshot/Controller/Full/Ajax.php(309): Snapshot_Helper_Restore::from('/homepages/30/d...')
#2 /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-includes/class-wp-hook.php(298): Snapshot_Controller_Full_Ajax->json_start_restore('')
#3 /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters('', Array)
#4 /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#5 /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-admin/ in /homepages/30/d507464059/htdocs/clickandbuilds/DessertsDel/wp-content/plugins/snapshot/lib/Snapshot/Helper/Restore.php on line 306"

which actually points to the line that should... "extract manifest".

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