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

• Visit a page diff with same oldid and diff, i.e. https://meta.wikimedia.org/w/index.php?oldid=111111&diff=111111
• Press "Mobile View" link at the footer

What happens?:
There will be an error said:

Bad revision
The ID for the revision you requested does not exist.
This is usually caused by following an outdated diff link to a page that has been deleted or a diff link containing invalid characters.

When this bug occurred, the URL is https://meta.m.wikimedia.org/wiki/Special:MobileDiff/111111...111111

What should have happened instead?:
It should show the correct mobilediff page

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):