Not all objects in request/task &1 were locked

What causes this issue?

Request/task &V1& could not be locked completely because some objects
caused problems.

System Response

The function was not completed correctly. Not all "lockable" objects
were locked.

How to fix this error?

Check the "lockable" objects that could not be locked using the error
log. Also refer to the long texts of the messages.
Correct the error and then repeat the function.

Error message extract from SAP system. Copyright SAP SE.