UglifyJS reproduction

input.js

function fn1() {
    return function fn2(ARG1) {
        return callApi({ foo: ARG1 })
            .then(handler);

          function handler(response) {
              const obj = { PROP: response };
              return (inlinedFunction(obj.PROP))
                .then(fn3());
          }

      function fn3() {
        return WRONG_VARIABLE_AFTER_MINIFICATION(ARG1)
      }

    }

    function inlinedFunction(ARG1) {
        return callApi(ARG1)
    }
}

output.js

function fn1() {
  return function(ARG1) {
    return callApi({ foo: ARG1 }).then(function(response) {
      return ((ARG1 = response), callApi(ARG1)).then(
        WRONG_VARIABLE_AFTER_MINIFICATION(ARG1)
      );
      var ARG1;
    });
  };
}

package.json

{
  "name": "uglify-repro",
  "version": "1.0.0",
  "main": "index.js",
  "author": "Stephen Jennings",
  "license": "MIT",
  "scripts": {
    "build": "uglifyjs input.js -o output.js --compress && prettier --write output.js"
  },
  "dependencies": {
    "prettier": "^1.13.5",
    "uglify-es": "^3.3.9"
  }
}