Elasticsearch 7 + MySQL8: cron not reindexing block title or text block content

[Dianne Tennent]

Internal Catalyst info: This bug is related to line 27 on the Elasticsearch testing spreadsheet on Alfresco 'Full text search' tab

MySQL8+Firefox on main

To replicate:
1. Add a person to the site
2. Enable Elasticsearch 7, select all artefact types and index the site
3. Masquerade as the person you added
4. Create a page, add a text block with a unique word in the title and a unique word in the text content.
5. Run cron to reindex the site
6. Type that unique word into the search field and click search

Expected:
 - Page containing text block appears in search results, or the text block itself

Actual:
 - No results

This issue does not occur with Postgres.

Further notes:
On MySQL, when running cron to add new items to the search index, it did not appear to run functions related to Elasticsearch 7, so this may be part of the problem. Also, when cron didn't work, I tried clicking 'Reset' to reset all indexes on the plugin config page, and the page just hung on "loading..." / "Processing..."