Since HCL doesn't consider this as bug for whatever reason, I just copied it here in the hope they'll at least care more on this platform:
We noticed that Wiki pages after a certain length got a second scrollbar on the right side (see screenshot I attach after submitting the ticket). This is NOT from the browser. I see the position as a bug because there is (wasted) space between the scroll bar and the end of the browser-window.
This occurs on a certain width, for me it's a standard full hd screen. So I assume the waste of space is even larger on higher resultions like WQHD or 4k.
We were able reproduce the problem as my screen resolution is high enough to widen the browser beyond the maximum currently available for Wikis. When that point is reached, the scrollbar remains to the right side of the Wiki content and not the right side of the browser window. This is expected behavior in this scenario. You may need to open an enhancement request to have development consider changing it. Below is the link for the enhancement ideas.