I have encountered another manual reading failure error — if you actually read the Cypher documentation for WITH, it clearly states that entering a WITH block creates a new scope into which previous variables are not imported. Unless you specifically include them. You can individually include variables in this new scope (WITH oldvariable1, oldvariable2, newSomething as newvariable1) or just use * to include all previous variables.

Doing neither will produce an error that a variable that you are absolutely positive exists does not, in fact, exist.