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

• Open a page that requires reauthentication to edit using the mobile editor. In my case, this editor is loaded by default only on RawHTML pages like https://fr.wikipedia.org/wiki/MediaWiki:Gadgets-definition?useformat=mobile#/editor/0 . This editor is loaded whether I click the default action=edit&section=0 button, the action=edit&section=all button or manually type only action=edit in the URL. On the other hand, when editing JS or CSS pages on mobile, 2010 editor is used automatically and there are no reauth issues with thes pages.
• Do a null edit
• Try to save

What happens?:
Permission error even if you do have the relevant rights.

capture is from desktop using ?useformat=mobile. Same issue on an actual mobile.

What should have happened instead?:
Reauth flow is triggered to allow the edit.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):
browser: Opera
My editor settings: