A weird issue in macOS’ Fast User Switching feature is causing an unknown number of Apple silicon Mac computers to spontaneously display the screen saver and log out the user. The unusual software bug leaves the user unable to dismiss the screen saver, forcing them to restart their computer in order to regain control of their desktop workspace.

A new bug hits M1 Mac owners

According to user reports Reddit and Apple Community Discussions, the problem is affecting an unknown number of owners of M1 Macs who have two or more accounts set up on their computer and use the Fast User Switching feature to quickly switch between them. “What happens is that a user can be working at their Mac when, without prompting, it displays a screensaver — and logs the user out,” AppleInsider writes.

You can turn Fast User Switching on or off in System Preferences → Users & Groups

One Reddit user wrote:

I have a brand new M1 MacBook Pro running macOS 11.1 and I’m having a small yet annoying issue. At random times, while in the middle of working, my machine will suddenly activate the screensaver. I cannot click out of it, and my keyboard does nothing. The only fix I’ve found is to close the MacBook for 4-5 seconds, then open it and upon reloading in, it fixes itself.

Setting the screen saver to Never appears to solve the problem.

Some people are reporting that their computer continues to spontaneously display the screen saver and log them out even with the screen saver disabled. And there appears to be at least one user who has experienced this issue on an Intel-based Mac.

Problematic Fast User Switching

Fast User Switching allows you to quickly switch between multiple user accounts on your device, including a Guest account. When this option is enabled, more than one user can stay logged in at the same time. It’s a very convenient security feature to have.

How to enter macOS Recovery on M1 Macs

Unfortunately, Fast User Switching comes with problems of its own. Fast User Switching was especially problematic on macOS Catalina due to issues with using Touch ID authentication when switching between multiple active user accounts. On a related noted, as iDownloadBlog reported last week, Apple is now blocking owners of M1-equipped Macs from side-loading unsupported iPhone and iPad apps onto their machines.