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CLJacked Author

Level 1

8 points

macOS Big Sur 11.5.1 freezing after update with iMac 27-inch, Late 2015

Hello!

My iMac 27-inch, Late 2015 is extremely sluggish (3-5 minutes for a Finder window to open with every app closed) and freezing (perpetual spinning beach ball) after attempting to open any app. I can't open Terminal.app to see if the update had been fully installed (System Preferences and About This Mac displays it has).

When previously installing macOS Big Sur 11.5.0, six days ago, the installation failed multiple times, stating the Download wasn't available. Attempting to redownload failed. Eventually, I rebooted the system, then everything seemed fine, and macOS Big Sur 11.5.0 was installed. It operated fine after this.

I tried starting in Safe Mode 35 minutes ago, and it's just now finally gotten out of the "spinning beach ball" freeze mode, yet attempting to open anything freezes the iMac again.

I guess I will try and start up from macOS Recovery and get back to Big Sur 11.5.0 and then reinstall Big Sur 11.5.1? -- But if this doesn't work, can Time Machine downgrade to Catalina 11.4.0 from Big Sur 11.5.0?

I hope I don't have to do a system hard reset, clean, and reinstall.

Many thanks,

Chris

iMac (Retina 5K, 27-inch, Late 2015)

- Processor: 4 GHz Quad-Core Intel Core i7

- Memory: 32 GB 1867 MHz DDR3

- Graphics: AMD Radeon R9 M395X 4 GB

Posted on Aug 8, 2021 5:53 PM

Top-ranking reply

PRP_53

Level 10

91,663 points

Posted on Aug 9, 2021 4:22 AM

Firstly, reinstalling Big Sur via Recovery Mode will not downgrade to Big Sur 11.5.0 as that version is not longer available.

Secondly, the Recovery Mode will only re-download the most recent version which is Big Sur 11.5.1 and will install over the existing version. It Will replace any missing or corrupted System files and not touch your Applications, Settings and personal documents.

The messed up previous installation may have presented issues wherein additional Volumes have been created and occupying unneeded space on the drive.

As for Time Machine Backup and reverting - Question. Has the existing TM Backup drive been used since the Big Sur Installation OR has it remained unused ?? Important question as this may be a factor in Reverting to Previous Operation System

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macOS Big Sur 11.5.1 freezing after update with iMac 27-inch, Late 2015

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