My interpretation is that Webklex PHP-IMAP has been implemented into ITFlow but that OAuth2 support (that Webklex PHP-IMAP facilitates) has not yet been added to ITFlow.
EDIT: My other interpretation, based on the code, is that the "Test IMAP Connection" function in Admin > Mail does not use Webklex PHP-IMAP. Could this create a situation where the "Test IMAP Connection" function works correctly, but cron_ticket_email_parser.php does not?
Also: Webklex PHP-IMAP failures do not appear to log to Admin > Audit Logs like mailparse did.