Steps to replicate the issue (include links if applicable):

• Browse https://fr.wikipedia.org/wiki/Portail:R%C3%A9chauffement_climatique
• Purge it: https://fr.wikipedia.org/w/index.php?title=Portail:R%C3%A9chauffement_climatique&action=purge
• Refresh

What happens?:
Page switches from Monobook to Vector 2022 after purge, then switches from Vector 2022 to Monobook after refreshes.

What should have happened instead?:
Page stays in Monobook.

Other information:
On Chrome, see: https://commons.wikimedia.org/wiki/File:Monobookvector2022.webm