This appears to be a new regression. It didn't used to do that. Should be easy to fix.

Change 302296 had a related patch set uploaded (by Bmansurov):
Do not show the revision info twice

https://gerrit.wikimedia.org/r/302296

@bmansurov's patch fixes this problem but introduces a less severe regression which I think should be fixed as part of solving this bug (I would have -1ed the patch but I felt it was a step in the right direction).

The breadcrumbs now appear in the warning box even though they are not a warning.

• Put $wgNamespacesWithSubpages[0] = true; in LocalSettings.php
• Create page "Breadcrumbs"
• Create page "Breadcrumbs/2"
• Edit "Breadcrumbs/2"
• View "Breadcrumbs/2" with the first revision

Change 302296 merged by jenkins-bot:
Do not show the revision info twice

https://gerrit.wikimedia.org/r/302296

@Nirzar what do you think about the screenshot at T139930#2513005? Should we not wrap the revision info in a warning box? The content doesn't seem like it's a warning.

Compare before:

As long as warning box has neutral styling (grey) i think it's a good idea to separate it from the actual content of the page.

Change 302485 had a related patch set uploaded (by Bmansurov):
Wrap revision info and nav in a div for easy formatting in MobileFrontend

https://gerrit.wikimedia.org/r/302485

Change 302486 had a related patch set uploaded (by Bmansurov):
Do not wrap breadcrumbs into a warning box

https://gerrit.wikimedia.org/r/302486

Change 302485 merged by jenkins-bot:
Wrap revision info and nav in a div for easy formatting in MobileFrontend

https://gerrit.wikimedia.org/r/302485

Change 302486 merged by jenkins-bot:
Do not wrap entire subtitle on diff pages in a warning box

https://gerrit.wikimedia.org/r/302486

Signing off. I don't have a screenshot from before the first patch was merged, so I can't recall the exact nature of the change. But stable and the provided links look okay and don't seem to be repeating elements.