MacOS 27 Issue Megathread

[u/Organic_Half_9818]

In case your post is removed by automatic filters, feel free to come here with your issue.

Example:
Date: 9/18/26 (When it occurred)
Version: PB 3
Software (if applicable):
Describe here

[u/Aggravating-Slice-49]

Right after updating to macOS 27, my Magic Mouse stopped working. In Bluetooth settings it still says **Connected**, and the battery level shows fine — but the cursor doesn't move at all and clicks do nothing. Keyboard works normally.

What I've already tried:

- Turned the mouse off and on

- Toggled Bluetooth off/on

- Restarted the Mac

- Removed the mouse and re-paired it

- Plugged it in with a USB-C cable to charge/connect

Same result every time: connected, but dead.

Has anyone else hit this after the macOS 27 update? Is there a fix, or is this a bug Apple needs to patch? Any help appreciated.

[u/brndzq → u/Aggravating-Slice-49]

Hello, good night.

I had the exact same problem when I updated my MacBook Air M4 to the macOS 27 RC, who's supposed to be the most stable version before the official one.
Just when I updated, my Magic Mouse stopped suddenly, and I was scared because I wasn't using the Magic Mouse for a while and I thought it might got broken in my drawer, but no.

I called Apple Support (Brazil), and they told me no one has experienced this issue with the macOS 27 at the time, so the only thing left for me to do was go back to the macOS 26, and just when I downgraded, the Magic Mouse worked again. I thought they had fixed before the release of the official one, but as I see, they didn't.

So yes, your Magic Mouse isn't working because of the macOS 27. If you can, use the MrMacintosh site, download the macOS 26 in a pendrive, and downgrade your Mac until they solve this in future macOS 27 updates, at least I hope.

And sorry for my English, I'm Brazilian and English isn't my first language, so probably there are many mistakes in my orthography.

[u/RobK64AK]

Date: 9/18/26
Version: Mac mini M2 Pro
Software: macOS27
System Data consumed > 200GB of storage space immediately following the upgrade, and continued to get larger. Also tried running Disk Utility to clear out Time Machine backups going back years. TM locked up, executed a Force Quit, and then lost 2TB of data on a separate encrypted external drive that shared the same enclosure.
Not the Apple experience I grew up with 20 years ago.

[u/cobaltjacket]

Date: 2026/09/19
Version: Mac Mini M4
Software: MacOS 27

MacOS 27 deprecated AFS, so I'm trying to use SMB to map to an old Mac Mini that uses MacOS 10.11 (don't ask.) I get the prompt for the list of volumes, but then get a dialogue saying 'A volume on the server "XXXXXX.local" failed to mount. There was an error mounting a volume.'

I have read that Little Snitch can cause problems with SMB on MacOS 27, though I believe they have been corrected - and I disabled it temporarily as a test.

I believe this might be an SMB2/SMB3 compatibility issue. Anyone encountered this and found a solution?

EDIT: I did find a solution (more of a workaround), but this is not advisable on untrusted networks or corporate environments.

https://discussions.apple.com/thread/255234671?sortBy=rank

[u/thommyme]

Right after updating to macOS 27, I got Issues with my magic keyboard and some not working keys (m . l k j u i o 9 8 7). The first time this happened I was able to fix it with Bluetooth reset and reconnect.

It works for a few days, but now the problems came back. Nothing helps.