Find My window makes WindowServer and kernel_task use high CPU (IOSurface "fClientTask not found" errors)

If your Mac feels sluggish on macOS Tahoe and Activity Monitor shows high WindowServer and kernel_task CPU, check whether the Find My app is open.

On my M1 MacBook Air (macOS 26.5.1), whenever the Find My window is on screen, the kernel logs this error about 80–120 times per second:

(IOSurface) SID: 0x0 task: <private> buffer: 0x0 buffer->fClientTask = 0x0 not found

It comes from WindowServer's main thread, once for every frame drawn. Over about 7 hours it logged roughly 2.6 million errors. During that time WindowServer used about 73% CPU and kernel_task about 105%. Restarting didn't fix it, because Find My reopened at login.

How to check if you have it:

Step 1: Open Terminal and run: log stream --predicate 'eventMessage CONTAINS "fClientTask"'

Step 2: Open Find My. If lines scroll continuously, you're affected.

Step 3: Hide Find My (Cmd-H) or quit it, and the errors stop immediately.

I tested every other app I had open one at a time, and only Find My causes it. Hiding the window is enough; it only happens while the window is visible.

Workaround: Keep Find My closed, or hidden with Cmd-H, when you're not using it. If Find My reopens at login, quit it or turn off "Reopen windows when logging back in".

I've reported this to Apple through Feedback Assistant (***) with sysdiagnose logs. If you see the same thing, filing your own report and mentioning that number helps Apple prioritize it.

[Edited by Moderator]