Workflow no. & cancel step &: Exception '&' at cancelation of work item &

What causes this issue?

When trying to cancel work item number <(>&<)>4, the error or exception
<(>&<)>3 occurred.

System Response

The work item specified above was not cancelled by the Cancel command.
The workflow continues to run. If there are other work items for the
workflow step <(>&<)>, they are cancelled.

How to fix this error?

Depending on the exception, the following actions are required:
The work item is currently in a processing state in which it cannot be
cancelled. Inform the current agent or responsible workflow system
administrator about the situation and, if necessary, have the work item
concerned cancelled manually.
When the work item was cancelled, notification of an agent failed.
Determine who the agent is and notify him/her, for example by e-mail.
Internal error 'Unknown WI status': Inform SAP.
A required database change when the work item was cancelled failed:
Repeat cancellation by hand.

Error message extract from SAP system. Copyright SAP SE.