I've just noticed that additional vertical (and horizontal) scrollbars are appearing when reviewing questions in the "First Posts" review queue. I've not noticed it in other review queues (but I've not seen/tested them all).
This seems to be reasonably "unique" to Webmasters SE as far as I can tell (or maybe not?). At least I don't see it on StackOverflow, ServerFault, SuperUser, WordPress and Android Enthusiasts. Although I do see the scrollbars on "English Language & Usage" and WebApps also.
The scrollbars only seem to show when reviewing "questions". (When reviewing an "answer" then there is naturally a question below it that stretches the container and avoids the scrollbars from showing.)
I think these scrollbars may have started with the introduction of the "New contributor" badges immediately below the users signature panel. If you
display:nonethese badges then the scrollbars are also removed.
The "First Posts" review queue naturally gets all the "new contributors" so that may also explain why I'm only seeing the scrollbars in the "First Posts" review queue.
Chrome (Version 68.0.3440.106) on Windows Desktop. Browser window is maximised on a 1920 x 1200 pixel display, viewing at 100% (ie. no zoom).
The above screenshot is cropped from a larger 1920 x 1200 pixel image: