Had to think back quite a bit, but yes - I have seen it with HMC software 4.3.2. Seems the communication gets lost between the HMC and managed system.
Either use HMC GUI to remove server, and add server again, or run the compareable command line commands after logging in via ssh (on HMC).
NAME
rmsysconn - remove system connection
SYNOPSIS
rmsysconn -o {remove | reset}
{-m managed-system | -e managed-frame | --ip IP-address}
[--help]
DESCRIPTION
rmsysconn removes or resets a connection from the Hardware Management Console (HMC) to a managed system or a
managed frame.
NAME
mksysconn - create system connection
SYNOPSIS
mksysconn --ip IP-address [-r {sys | frame}]
[--passwd password] [--help]
DESCRIPTION
mksysconn establishes a connection from the Hardware Management Console (HMC) to a system in the network and
adds the system to the systems managed by the HMC. If a connection to the system cannot be established
because the network is down, the service processor for the system is down, or too many other HMCs have
already established a connection to the system, the system will be added as a managed system which is in the
No Connection state.
NAME
lssysconn - list system connections
SYNOPSIS
lssysconn -r all [-F [attribute-names] [--header]]
[--help]
DESCRIPTION
lssysconn lists connection information for all of the systems and frames managed by this Hardware Management
Console (HMC). Connection information for all systems and frames to which this HMC is connected or attempt?
ing to connect is listed.
OPTIONS
-r The type of resources for which to list connection information. The only valid value is all for all
managed systems and managed frames.
-F A delimiter separated list of attribute names for the desired connection attribute values to be dis?
played for each resource. If no attribute names are specified, then values for all of the connection
attributes for the resource will be displayed.
Hope this helps