Support for unsafe ciphers was removed as part of a security update in EcoStruxure IT Gateway version 1.8.0. Devices using the Redfish protocol must now support 2048 bit certificates.
Devices that do not meet this requirement do not discover in Gateway 1.8.0 and newer. There is no indication of a certificate error when you run a new discovery.
When you update your Gateway from a previous version, Redfish devices are listed as offline.
Install a new certificate on the Redfish device that supports 2048 bit server certificates.