I visit this site on a small screen and hence I zoom to 150%. There has never been a scrollbar because of this before. However, now I have a horizontal scrollbar. Has the width of the sidebar changed? I'm not asking for anything to be done about this since that would be pretty unreasonable (though it is annoying because the next zoom option makes the text too small), just asking for confirmation.
Yes, there was a recent change: see We're standardizing the sidebar width at 300px on all sites. The announcement was featured in the aforementioned sidebar on all sites for two weeks, January 7-20.