MacOS Big Sur 11.5.2 update fail

If this update is for Big Sur 11.5.2 the error message can be misleading. There are factors like poor Wifi connection, slow wifi connection, too many other people downloading at the same time and Apple Severs are overloaded, Software on the computer interfering with the download process, running behind a VPN, AntiVirus Software and or / if via wifi too many Other devices using the wifi at the same time reducing the Bandwidth to you computer.

Best Results are via Ethernet Cable to Router

There are several ways to download the Big Sur 11.5.2 update. 

1 - Connect to Router via Ethernet connection and restart the computer in Safe Mode and then open the Apple Apps Store and get the Full Installer of Big Sur. It will be the 11.5.2 version and once downloaded run the installer from the Applications folder.

2 - Resart the computer in Recovery Mode ( INTEL Command + r ) and choose Reinstall macOS. It too will download the full Installer and commence the installation. For M1 CPU the Recovery Mode is Here

3 - This method may seem unnecessary but sometimes the Router Restart clears Network issues from ISP to Apple Servers

Shutdown Router. Shutdown computer and disconnect all External Drives. Restart Router. Connect to Router via Ethernet Cable. If via Wifi - Disconnect all other Devices using the Wifi - want the Maximum Bandwidth only for this computer. Restart computer in  Safe Mode. It does a Repair Disk, Clear System Cache files and only load Apple Software, extensions and Fonts. Will load slowly - Normal. Once Logged in - open Apple Apps Store and  Get the Full Version of Big Sur. It will take some time and several pauses will occur - normal. Countdown clock may say 15 minutes but in Real time may be 30 minutes. Same goes for clock at 10 minutes could be 20 minutes in Real time. Eventually , Full Installer will download and a New Application in Applications Folder will present called Install Big Sur. Stop there and perform a Time Machine Backup. If desired - have an External Drive - Copy & Paste the Install Big Sur Application to external drive for future usage - making a Bootable Installer. Now run the Installer.

Have found this method more reliable than the Software Update which is very iffy at best

Are there any AntiVirus, Disk Cleaner, Optimizers, Defrag, VPNs etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation.

Could might several issues at play, FileVault if enabled, AntiVirus Software that was installed before the update was being applied and is interfering with the update process, lack of empty space, some third party extension or font.

If it has not cleared up as of this writing, suggest shutdown by whatever means required even power button. Disconnect all external devices and connect to charger. Restart the computer in Safe Mode . This should do a repair disk, clear system cache files and only load Apple Software, extensions and fonts. This eliminates all 3rd party software from loading and may or may not allow the update process to complete - hopefully successfully :-))

In my experience this problem occurs when using a wireless connection. Wi-Fi is just too slow for these very large files. Put the old installer into the Trash and empty it, then connect to the modem/router with an Ethernet cable connection and do a new clean download. it should take up to an hour, more or less and then another 45 minutes, more r less, to install with several automatic restarts. Good luck.