Symptom
Procedure of changing FTD management IP address include information:
Changing the IP address will not affect the current connection. However, if the device or Management Center reloads, then the connection needs to be reestablished. You need at least one of the devices (Management Center or managed device) to have the correct IP address of the peer.
Procedure is described in FMC Configuration guide:
https://www.cisco.com/c/en/us/td/docs/security/firepower/623/configuration/guide/fpmc-config-guide-v623/system_configuration.html#id_46848
Described behavior is incorrect because changing the IP address will affect the current connection immediately.
For restore connection between FTD and FMC, you must change the management IP address of the device in the Management Center; see Editing Device Management: https://www.cisco.com/c/en/us/td/docs/security/firepower/623/configuration/guide/fpmc-config-guide-v623/device_management_basics.html#ID-2242-00000e62
