1826767 - 'Could not check credentials...Connection refused' when upgrading HANA using SUM

The self update of SUM (Software Update Manager) has finished successfully. After restart of SUM, it is then no longer possible to connect to SUM using the lifecycle management perspective of the HANA Studio. The following error is displayed:

Error:
Could not check credentials provided for user <sid>adm on host <hostname>.

Error Details:

Could not check credentials provided for user <sid>adm on host <hostname>.

Could not connect to SAP host agent on host <hostname>. 
Check that it is
running.
HTTP transport error: java.net.ConnectException: Connection refusedConnection refused

The sapstsrv process is running in the system and accepts http connections.

• SAP HANA Database.
• Using SUM (Software Update Manager) as outlined in the Automated Update Guide for your HANA Revision.
• Performing selfupdate of SUM that had a version smaller than SP05.

Execution of operation update-newdb-server failed; port 1129; https; Automated Update Guide for; sapstarsrv; web services; , KBA , HAN-LM-PLT , SAP HANA Platform Lifecycle Management , HAN-DB , SAP HANA Database , Problem