If you getting errors like NIEHOST_UNKNOWN from your ICM logfile then you should check more deeply your log file to find requested connection address informations.

There is an example issue which i had a couple of days ago ;

Created Worker Threads nearly full ;

SMICM Status looks like ;

DEV_ICM log file details ;

As you can see , problems are ;

arcdev.wdf.sap.corp

hs2086.wdf.sap.corp

Then go to transaction OAC0  – Display Content Repositories

Find Storage Type : HTTP Content and check the details to be sure

arcdev.wdf.sap.corp

hs2086.wdf.sap.corp

Delete these entries on transaction OAC0  – Display Content Repositories

Restart ICM via SMICM transaction

Finally your SMICM should look like these and all errors will be gone ;