1. Open minimal page at https://wikitech.wikimedia.org/w/index.php?title=Sandbox&oldid=1983803&veaction=edit
2. Place cursor in heading.
3. Insert template: Anchor

Expected:

For the editor to show a puzzle piece with "Anchor" where the otherwise-invisible template resides.

Actual:

It is invisible.

Other:

The same steps on mediawiki.org work as expected, e.g. at https://www.mediawiki.org/w/index.php?title=Project:Sandbox&oldid=5229096&veaction=edit, where I've prepared the same minimal test case. As such, I suspect that either something is working incorrectly with how this wiki is configured or customised (e.g. VE config, Parsoid settings, or other core settings that affect VE), or that the template on Wikitech has triggered a bug in VE that would be reproducible on other wikis as well.