Status records with status 51 after status 53

What causes this issue?

The application function module controlling the ALE inbound processing
has passed several status records to ALE. The status of the last of
these was '51'. Before this, a status of '53' was passed.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

How to fix this error?

If you have written the application function module yourself, you need
to change the program.
If the problem occurs in a function module from a standard application,
you should notify SAP.

Error message extract from SAP system. Copyright SAP SE.