Workaround could be provided to fix this issue.
1) generate a support bundle for both probe and portal
2) export configuration of probe FxM through its web console: Configure | Appliance | Database | Export Configuration
3) From the portal web console: Help | System Information | click "remove" besides the probe in question
4) double check the probe type setting on the probe FxM is still effect: Configure | Appliance | Type
Please note that the above process will clear the monitoring server & protocol configuration from the portal. That's why we need to do step 1) & 2) in order to keep a record for previous configuration. You need to manually restore those monitored IP/protocol settings with help of technical support.