1664214 - Upgrade is not able to start or stop an instance because of an "HTTP error 401 Unauthorized"

During the upgrade, the upgrade tool is unable to start or stop the shadow instance or the normal instance.
At the log file "<upgrade_folder>/abap/log/SAPup.ECO", the following error is seen (at the end of the file):

EXECUTING <...>/abap/exe/sapcontrol
(<...>/abap/exe/sapcontrol) -prot NI_HTTP -host
<server> -nr $$ -function StartWait 600 10

<date and time>
Start
FAIL: HTTP error, HTTP/1.1 401 Unauthorized

"<...>" stands for the upgrade folder
"<server>" is the server name on which the upgrade is being performed
"$$" stands for the instance number of the instance being started/stopped by the upgrade

SAP Note 1565645 has been checked, however the issue still persists.

Note: for SUM, see SAP Note 1600846.

• Product / Release independent
• Client Server Technology - Startup Service

Upgrade, Shadow Instance, Sapcontrol, Sapstartsrv, Unauthorized, HTTP error, 401 unauthorized, Instance, Stop, Start, Start profile, Instance profile, Service/protectedwebmethods , KBA , BC-CST-STS , Startup Service , BC-UPG-ADDON , Upgrade Add-On Components , BC-UPG-TLS-TLA , Upgrade tools for ABAP , BC-UPG-OCS , Online Corr. Support (Tools:Supp.-Pack., Addon Install/Upgr) , BC-UPG-OCS-SPA , Support package tools for ABAP , BC-UPG-TLS-TLJ , Upgrade tools for Java , BC-UPG-OCS-ZDM , Near Zero Downtime Maintenance , Problem