Variant table in KB &1 &2 cannot be activated during system upgrade

What causes this issue?

The generation of a knowledgebase runtime version requires the creation
of one or several variant tables on the database.
The system is currently in an upgrade phase which can lead to activation
errors for database objects.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

Generation of the knowledgebase runtime version is aborted.

How to fix this error?

Repeat the generation of the knowledgebase runtime version when the
system upgrade is finished.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.