It seems that since a couple of weeks ago, general pages with the sizeToParent option once again get the wrong height, resulting in really uncomfortable scrolling behaviour.
As you can see in the video, while the page loads and while resizing the sidebar, the content jumps around a lot due to a horizontal scrollbar appearing and disappearing.
A vertical scrollbar is shown for the whole page, which is unnecessary since the page should have the height of the screen, but seems to be a few pixels higher. The vertical scrollbar covers the iframe, hiding any scrollbars that are present inside the iframe.
PS: It would be really nice if it were possible to upload such videos here directly!
This doesn’t only affect general pages but now also the Admin Page Connect module. I don’t really know when it started but some time back in September this wasn’t an issue yet.
Actually, this unnecessary vertical scrollbar exists on every administration page and not only on those containing an IFrame with the Admin Page Connect module. When having a look into the developer tools the cause seems to be this CSS rule
There is an inconsistency between the height and top attributes (56px vs 58px) which causes the vertical scrollbar to be shown. In addition the width attribute also looks a bit suspicious because the 100vw usually don’t take the size of vertical scrollbar into account. This probably leads to the horizontal scrollbar to appear and might also trigger the flickering of the horizontal scrollbar when the page height changes (e.g. due to async loaded content). This could for instance be observed in the UPM admin page.