I had a case where I tried to check that a function was called with an object that contained a key whose value was a snapshotted string, so I used one of the "satisfying" assertions in -sinon. The following is a simplified reproduction case:

const expect = require("unexpected")
  .clone()
  .use(require("unexpected-snapshot"));

const makeSomeStuff = () => "foo bar baz\nbaz bar foo";

it("should work", () => {
  expect(
    [
      {
        stuff: makeSomeStuff()
      }
    ],
    "to satisfy",
    [
      {
        stuff: expect.it("to equal snapshot")
      }
    ]
  );
});

Running mocha on the above in snapshot update mode as-is, I receive the following TypeError:

     TypeError: Cannot read property 'replace' of undefined
      at fixUnexpected (node_modules/unexpected-snapshot/lib/applyFixes.js:87:62)
      at Traverser.enter [as _enter] (node_modules/unexpected-snapshot/lib/applyFixes.js:209:26)

If I force the insertion point by modifying the expect.it to read expect.it('to equal snapshot', '') it gets further, but the injection of the snapshot removes the nested spec structure on the RHS and instead injects at the top level resulting in:

it("should work", () => {
  expect(
    [
      {
        stuff: makeSomeStuff()
      }
    ],
    "to satisfy",
    expect.unindent`
      foo bar baz
      baz bar foo
    `
  );
});