errors after update to 5.1.9

The following errors occurred after updating to version 5.1.9. The only way to stop the error was to either deactivate or uninstall and reload the previous version (3.something).

Warning: session_start(): open(…/tmp/sess_67ibi3t06mob704jmu0hka00d6, O_RDWR) failed: No such file or directory (2) in …/html/wp-content/plugins/email-before-download/admin/class-email-before-download-admin.php on line 148

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at …/html/wp-content/plugins/email-before-download/admin/class-email-before-download-admin.php:148) in …/html/wp-content/plugins/email-before-download/admin/class-email-before-download-admin.php on line 148

Warning: Cannot modify header information – headers already sent by (output started at …/html/wp-content/plugins/email-before-download/admin/class-email-before-download-admin.php:148) in …/html/wp-admin/includes/misc.php on line 1116