SharePoint spacer resizing handle not available

Prior to the new year, SharePoint spacer web parts had handles that could be used to resize the height of the spacers no matter the width of the page section within which the spacer was used.

However, sometime in the new year, I noticed that I had lost the ability to resize spacers in 1/3 sections (see attached image). (The handle is visible when the spacer is in single and 2/3 sections; see attached images.) I can't resize spacers using either my mouse or the arrow keys on my keyboard. This happens across sites.

Any idea what is going on?