Syntax error prevented CDS-activation for Enterprise Search

What causes this issue?

In the After-Import step of transportation object SESA, CDS-views
annotated by @EnterpriseSearch are activated for Enterprise Search.
Coding required in this process has syntax errors. This may happen e.g.
during an upgrade.

System Response

The system skips this activation step in order not to interrupt the
import process. For this reason, the message is issued as a warning,
although it actually represents an error.

How to fix this error?

First, correct the syntax errors, using the transactions SNOTE and SPAM/
SPAU-tools.
Make sure that all notes are applied completely and correctly.
Then, go to transaction SE24; enter CL_ESH_CDSABAP_ACTIVATION as class
name and press F8. Hit the ?Execute Method?-button for method
ACTIVATE_ALL; press F8 without any changes on the parametrization.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.