Answer
A 'simple bind failed' error specifically on the LDAPS port usually comes down to one of three things: the SSL/TLS handshake itself isn't succeeding (commonly because the AD server's certificate isn't trusted by the IFS server, or the certificate chain isn't properly installed), the bind credentials/password being used are actually incorrect (easy to overlook since plain LDAP working doesn't confirm the same credentials are correctly configured for the LDAPS bind), or port 636 isn't actually open/reachable from the IFS server (a firewall or network path difference from port 389). Working through SSL trust, credentials, and network reachability in that order is the fastest way to isolate which of the three is actually causing it.