Steps to replicate the issue:
Visit meta:Movement Insights using Parsoid.

See that the "Phabricator project" tag in the top right displays raw template code ("Phabricator project: [[phab:tag/{{{1}}}/|#{{{1}}}]]") rather than the rendered template. The legacy parser displays it correctly ("Phabricator project: Movement-Insights").

The wikitext at issue is {{Ptag|Movement-Insights}}, which uses the Ptag template).