Issue with email.send(): relatedRecords object fails silently and does not update via transactionId

@NApiVersion

Hello gurus -

I have a Map/Reduce script to send cancellation emails based off of a saved search. The email is sending just fine, however the

relatedRecords

object doesn't seem to work, when using the key

transactionId

, however when using

entityId

, it works fine and logs the email under the customer's Communication -> Messages subtab.

Has anybody experienced this before? Any idea if I'm doing something wrong? Here is the entirety of my code, any help or insight is appreciated!

 /**   * @NApiVersion 2.x   * @NScriptType MapReduceScript   * @NModuleScope SameAccount   */  define(['N/email', 'N/search', 'N/render', 'N/record'],    function(email, search, render, record) {            var department_map = {              15: {                  templates: {                      1: 301 // RISKIFIED DECLINED (KW)                  },                  author: 113746, // Customer Care                  template_vars: {                      '%SALESCHANNEL%': 'KegWorks.com'                  }              },              35: {                  templates: {                      1: 302 // RISKIFIED DECLINED (BTB)                  },                  author: 21100362, // Customer Care BTB                  template_vars: {                      '%SALESCHANNEL%': 'BehindtheBar.com'                  }              }          };        function getInputData() {          return search.load({              id: 'customsearch_kw_cancelledorderstoemail'          });      }        function map(context) {          var searchResult = JSON.parse(context.value);          context.write(searchResult);      }        function summarize(summary) {          summary.output.iterator().each(function(res,v) {              res = JSON.parse(res);              var so_id = parseInt(res['id']);              var values = res['values'];              var email_address = values['email'];