We are implemented K2 system in our organization and in the last two months we have even purchased an Internet connector for users who don't in domain.
Recently, users who would connect via Internet Connector encountered a K2 authentication fault - the system thinks but doesn't respond.
Architecturally users turn to DMZ and the DMZ displays a "Mirror" of the production server (server in domain) on which the application is installed.
Users who work in domain have no problems at all, only users who are connected via the Internet Connector.
We performed tests (TelNet) and run traffic tests on the servers for a number of ports, the main port 5555, where we get an error message that we can't reach the production server through the DMZ, and again, this only happens in port 5555 and not in another ports.
I would like to emphasize that after we restarted the servers, we turned off and on the services - the system worked fine and TelNet was fine for port 5555.
I would be happy for help - maybe we need to change something on the server, maybe set up work with IIS level loads.