Data inconsistency in substitution "&", step "&"

What causes this issue?

During ABAP code generation, a data inconsistency was found in the &V1&
substitution.

System Response

The corresponding ABAP code was generated for the Boolean statement,
but it could be, that the valuation of the statement could lead to an
unexpected result.

How to fix this error?

Check and correct the &V1& substitution using the substitution
maintenance.

Error message extract from SAP system. Copyright SAP SE.