Please check optical module (s). You must use same transceiver to port 45,46,47,48. If you have 2 kind of transceiver on that ports you can't make iStack work. Based on typical issues encountered with optical modules in daily switch applications, this document summarizes basic troubleshooting steps for resolving common faults: 1. In device interconnection, this often indicates that the interface failed to start up properly. Those messages tell you what the switch detected (authentication mismatch, bad EEPROM, unsupported part number, PHY disagreement) and point to a small set of concrete checks. An optical module is a critical component in modern optical communication systems, directly affecting transmission stability, network reliability, and operational efficiency.