When you are saying that you have "migrated successfully", are you referring to replicating Gaia configuration only?
JE: full successful export of the database and successful import in R80.40, then migration to R81.10, also successful, no errors presented.
Can you confirm that SIC is working between management and the gateway?
JE: Being in the same appliance, the SIC is working fine.
Can you verify that the topology settings of the gateway object are correct?
JE: They are as they were in the previous appliance, and discover topology matched the interfaces as they were.
Can you verify that you have changed the appliance model and version to 6200 and R81.10?
JE: Yes, all represented correctly.
Is policy installation on the gateway succeeding and you are losing the ability to connect to it via WebUI and SSH afterwards?
JE: Policy installation is successful and just after deployment that we loose ability to connect to WebUI and SSH, but we can use the SmartConsole to access the appliance, modify the policy and deploy it.
Is the workstation from which you are attempting to connect located on the same internal network as the internal interface of the gateway or is that connection being routed to it?
JE: Yes, same flat network: 10.1.0.0/16
Is your management server on the same internal network as the internal interface of the gateway or is it too, routed to it?
JE: It is an standalone appliance, so both management and security gateway are in the same hardware,
Simple example diagram (with fake public IPs) could be helpful.
JE: Simple diagram in ASCII here 😉
10.1.1.253/16 <-eth1->[CP6200]<-Mgmt->84.x.x.x/29 <-> Colt Router <-> The Internet
Note: eth1 assigned as the management interface, obviously.
Not sure what is wrong here, but all expert help would be highly appreciated.