Table of Contents block does not list headings until after the page is saved

[tkimnguyen]

When I add a TOC block to a page, followed by one or more Heading blocks, the TOC block remains unchanged. Only after I save the page, then re-edit the page, and if I click on a Heading block will the TOC block get updated to show that heading block. I have to do that for every heading block.

See here for screenshots:
https://community.plone.org/t/what-is-the-table-of-contents-volto-block-meant-to-do-maybe-buggy/20378