Red menu bar in Sonoma

Strange things happen in macOS. Today’s strangeness is novel to me: a red menu bar. If you can explain why it appears on my Mac running Sonoma, I’ll be eternally grateful.

Every so often, apparently out of the blue, the menu bar on my iMac Pro running macOS 14 turns red, and loses all the menus from its left end, but not its right.

This Mac runs fairly permanently with Stage Manager active. The red menu bar usually appears when switching between Stage contents, shown here when bringing the X (formerly Twitter) app and Safari onto the Stage. While the new windows appear correctly, instead of switching to the correct menu for either of them, the menu bar turns red and loses the menus that should appear at the left, for the front app.

At first I presumed that this might be a graphics/display glitch, as my iMac Pro has an old graphics card, a Radeon Pro Vega 56. But when such glitches occur in graphics, it’s most unusual for contents like the app menus to vanish at the same time. It also recurs every few days, although the Mac is left running 24/7, and I have never seen it on any other of my Macs, although I don’t usually use Stage Manager on them.

I then wondered if this was a warning from macOS about some problem such as excessive memory use, and tried opening Activity Monitor as soon as the red menu bar appeared. Of course opening a new app brings Activity Monitor on Stage; as soon as that happens, a normal menu bar is resumed immediately, and there’s no sign of anything unusual or alarming in CPU or Memory tabs in Activity Monitor.

It happens sufficiently infrequently that turning Stage Manager off isn’t going to be a good way to see if that’s related, as I don’t want to work for days without Stage Manager in the hope that it might occur again. The one thing I haven’t yet tried is looking in the log, as Stage Manager changes are accompanied by copious log entries, so trying to identify anything abnormal from the log is going to be tedious and long-winded.

Can you recall seeing anything similar in a recent version of macOS? If so, did you discover its cause?

Thank you for all your suggestions, including the idea that Sonoma is shocked that anyone would still be running that ancient and buggy Twitter app, let alone using X/Twitter.