Since upgrading to macOS 27, my menu bar occasionally disappears entirely whenever I use full-screen apps, and the problem affects multiple applications across the system. Changing System Settings → Menu Bar → "Automatically hide and show the menu bar" has no effect, even when set to "Never." When the issue occurs, moving the pointer to the top edge does nothing, and Control-F2 or Fn-Control-F2 also fails to focus the menu. Restarting the Mac usually restores the menu bar temporarily, and force-quitting MenuBarAgent has worked once, but the problem later returns without an obvious trigger. I'm not using Bartender, Ice, Hidden Bar, iStat Menus, or any similar utility. Has anyone found a cause or reliable fix?
3 Answers
I ran into the same behavior. Pressing F3 to open the overview of all windows, then selecting any regular window, brought the menu bar back when I switched to a full-screen app afterward.
This appears to be part of a broader full-screen and multi-monitor problem in this release. I’ve seen external displays go black after moving a full-screen Safari window, and detached Safari tabs can produce badly positioned or unusable windows. Those issues make a system-level window-management bug seem more likely than a menu-bar setting problem.
The problem doesn’t affect every Mac consistently. Some users report no menu-bar issues, even on multiple machines, so it may depend on a particular display setup, window state, or upgrade configuration. Restarting or force-quitting MenuBarAgent can reset it temporarily, but neither seems like a permanent fix.

That worked for me too—thank you! It seems to reset whatever gets stuck in the full-screen window state.