Currently the (i) in Visual Editor "Page settings" for the Table of Contents setting reads:

• "You can force a table of contents that lists each heading on the page to appear on pages with fewer than THREE headings, or force it to not appear at all. By default, it will appear if the page has THREE or more headings."

Afaik, this should be "four" instead of "three" in both instances. According to WP:TOC and a quick test on en-Wiki, the minimum limit to display the ToC by default is 4 headers (regardless of their header level apparently), not 3.