This activity deletes a min. of one phrase in the value assignment

What causes this issue?

The value assignment you selected consists of phrases from passive
libraries or the phrase is not part of the phrase set assigned to the
characteristic.
There are several possible causes:
These values were loaded into the SAP System via the import of
specifications. You cannot mix imported and manually assigned value
assignments.
If the phrase used has been removed from the phrase set assignment, it
can no longer be used for value assignment.

System Response

The system deletes all value assignments with passive or invalid
phrases.

How to fix this error?

You can either:
Confirm the message; the system then deletes the phrases in value
assignment
Cancel this message; the system then undoes the action.

Error message extract from SAP system. Copyright SAP SE.