Nothing on storefront when using ElasticSearch 5

[nathanjosiah]

Preconditions (*)

1. Magento 2.3.3 regression Enterprise cloud environment configuration which uses ElasticSearch 5.x (for this bug I was using 5.6.16)
2. No stocks or sources configured
3. Simple product created under subcategory so it displays on storefront (just to show data displays before the steps below)

Steps to reproduce (*)

1. See product from preconditions visible on storefront
2. Create new source Test Source 1 with Contact and address data set
3. Create new stock Test Stock 1 with Test Source 1 assigned
4. Add new simple product name Simple1/qty 10/assigned to new source with qty 100/weight 1/assigned to the subcategory

Expected result (*)

✅ All products should be showing correctly

Actual result (*)

❌ All products missing from storefront

Notes

ℹ️ None of the error logs contain any errors related to this issue. This includes var/* as well as Elastic Search's logs.
ℹ️ According to @mkozell and @aljcalandra the nightly builds are using ES6 which is partly how this issue has gone undetected.

[ishakhsuvarov]

Duplicates #2470

[ishakhsuvarov]

Fix delivered to the Magento core in the scope of internal Pull Request.

Commit reference: 9687ccf68d7d6c8b6059e3bc018e28ac60915962