Process &1 variant &2 is referenced but is not a predecessor

What causes this issue?

Process &V1&, variant &V2& must precede process &V3& &V4& in the chain.
However, there is no connection between these two proceses.

System Response

The system is unable to activate the process chain.

How to fix this error?

Change process &V3& &V4& so that it no longer references &V1& &V2&, or
schedule process &V1& &V2& in the chain so that it precedes &V3& &V4&.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.