Result of operation & & & is multiline

What causes this issue?

The result of operation &V1& &V2& &V3& is multi-line. Container element
&V1& can only include one line, according to the container definition.

System Response

The Workflow cannot be processed.

How to fix this error?

Correct the operation in the workflow definition. Continue the
interrupted workflow processing.

Error message extract from SAP system. Copyright SAP SE.