PHP 8.2.10, Phorge at 7868ab3754fad13714640451d664d5bc71b7a02f.

Steps to reproduce:

1. Go to http://phorge.localhost/project/edit/form/default/
2. Create project with name Slug404Name
3. Successfully go to http://phorge.localhost/tag/slug404name/
4. Select Edit Details to go to http://phorge.localhost/project/edit/23/
5. Rename project to Slug404NameAlt
6. Successfully go to http://phorge.localhost/tag/slug404name/ which redirects to new primary slug
7. Select Edit Details to go to http://phorge.localhost/project/edit/23/
8. Remove slug404name from Additional Hashtags && in the Name field replace Slug404NameAlt with Slug404Name
9. Go to http://phorge.localhost/tag/slug404name/

Expected outcome:
Project page is rendered

Actual outcome:
404 error

Other comments:

• Explicitly adding the already-primary slug Slug404Name to Additional Hashtags on http://phorge.localhost/project/edit/23/ makes http://phorge.localhost/tag/slug404name/ work again, as assumed in https://phabricator.wikimedia.org/T224662#5223847
• Might not be the only one to reproduce but finally a way to reproduce. Upstreaming from https://phabricator.wikimedia.org/T224662 as we've ran into this several times.