Data locked by user & (display only)

What causes this issue?

You have attempted, in change mode, to access data currently being
processed by user &V1&.

System Response

The system rejected this access attempt because only one user can
change data at any one time.

How to fix this error?

Please either acknowledge the message to display the data, or cancel
processing and call the maintenance transaction later.

Error message extract from SAP system. Copyright SAP SE.