This impacts several projects including: Wikivoyages, cawiki, euwiki
Not sure why... but it would be useful for editing there :)
To reproduce:
Install WikidataPageBanner and MobileFrontend extension
Create a page "Test page" with text "{{PAGEBANNER:Agra banner Taj Mahal.jpg|originx=right}}" in the Vector skin.
Click preview and you'll see the banner in the preview.
Mobile site issue
Navigate to the mobile site using the 'Mobile view' link at the bottom of the desktop page.
Click the edit icon in the mobile mode for the same page.
Click next in the overlay
In the preview the banner is not present.
Wikitext editor issue
Enable the new wikitext editor feature
Click "Erakutsi aurreikuspena"
In the preview the banner is not present
Expected:
The banner should be rendering in the mobile editor and wikitext editor preview.