System.log error after latest Security Update 2020-005 for Mojave from Sep 24th 2020

I suggest;

1. System Preferences -> Software Update, turn off "Automatically keep my Mac up to date" at least until they fix this mess

2. Download and install the previous Security Update 2020-004 from https://support.apple.com/kb/DL2045

3. Then go to System Preferences -> Software Update -> More info... -> if there is anything there apart from Security Update 2020-005 then install that

Yes, 2020-004 included all previous updates. Safari 13.1.2 was released after that.

It's in the list here https://support.apple.com/en-us/HT201222 on 15 July 2020, and details here https://support.apple.com/en-us/HT211292

Apple have now withdrawn the 2020-005 update (and Safari 14.0) that's why you don't see it any more. No doubt they will release a fixed version at some point in the future, I think next time I'll wait for others to try it first :)

Due to it's Size my guess would be no, I'd start over...

Try reinstalling this in Safe Mode, but not using Firefox...

https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12

Safe Boot, (holding Shift key down at startup).

I usually don't have any problems with security updates, but last night was a nightmare after I ran it on my Mac Mini(2014) running Mojave. My computer was so slow to the point of unresponsiveness for all command and key inputs. After several attempts of restart and power on/off cycling, I thought that a rogue or malware update broke my computer. I ended up running a MacOS reboot from Time Machine and thankfully my computer was back to normal after the procedure. Apple should stop pushing this update to users and get it sorted out. I am still getting the security update notification as of this morning, and I just unchecked it and will ignore it from this point forward.

I had a similar experience.

I installed the update and immediately my 21.5" (late 2013) iMac became unusable (beach balling on every mouse click; my Time Machine backup disk showed NO backups had been made; EtreCheck showed MAJOR issues; etc., etc.)

I spent several hours running Apple H/W diagnostics, booted into Recovery Mode and ran Disk Utility on both my Macintosh HD and Time Machine backup disks;. No H/W errors or disk errors were reported.

I then used Recovery Mode to reinstall my last Time Machine backup image just before I installed the last Security Update, and now everything is operating normally again.

I have NO third party S/W installed on my iMac -- I have no idea why this particular update "bricked" my system.

Something is seriously wrong with the 2020-05 update. Installed on a 2015 Macbook Pro and it spun for an hour trying to shut down prior to install. I had to force shutdown. On startup, the install completed, and it appeared all was well. Then I wake it up a couple hours later and the fans are going nuts, Kernel task is using 600%+ and I can't fix it.

Restart, SMC reset, pram reset, Booting from another drive, booting from USB Mojave installer, wiping SSD and booting from either Mojave installer, or internet recovery.... all of them machine is slow as **** and fans are going nuts.

Since installing the update system log is being spammed with messages of the form "Class <name> is implemented in both <path1> and <path2>. One of the two will be used. Which one is undefined."

I get the same message when running some command line utilities. E.g.

$ softwareupdate --history

objc[1435]: Class AMSupportURLConnectionDelegate is implemented in both /System/Library/PrivateFrameworks/EmbeddedOSInstall.framework/Versions/A/EmbeddedOSInstall (0x115e39c58) and /System/Library/PrivateFrameworks/OSPersonalization.framework/Versions/A/OSPersonalization (0x115c9c358). One of the two will be used. Which one is undefined.

Something definitely isn't right with this update.

Agree with everyone else. Apple better take note. Hubs iMac (2.8ghz i5 - late 2015) has zero of anything installed, third party or otherwise. Literally web surfs and watches YouTube on it. He had automatic updates on and the install of this security update tanked the system. I too restored from a backup (AND TURNED OFF UPDATES) what a horrible release.

I ran Disk Utility from Recovery Mode to ensure that my Time Machine drive (external USB) was not corrupted, and then reinstalled from a Time Machine backup that I made a few hours before applying the update.

I chose the option to erase my HD and install both the Mac OS X system files and my user files.

I did not lose any data (Keychain PWs, Safari PWs, Mail accounts, Network setup, Documents, Apps, etc., etc.)

Add my machine to the list. Mojave has slowed my system down so bad that even the spinning beach ball takes time to show up.

Did I say it's now incredibly slow... as in sssssssssssssssssssssssssssssssssslllllllllllllllllllllllllllllllllllllllllooooooooooooooooooooooowwwwwwwwwwwwwwwww?

Mac Pro mid 2010 running macOS 10.14.6 (18G6032).

Thank you for the security update.. the machine is real secure now... no one would be able to do anything with it.

Recovery mode also worked for me. I didn't backup before installing the update, and I have "Backup Automatically" turned off, but apparently the install created a local Time Machine snapshot anyway.

So restarted with Cmd+R, restored from that, all is well again. No more syslog spam or duplicate class implementations, and Activity Monitor now shows about 3GB memory used on startup instead of over 8GB (that is probably what is causing the slowdowns reported in many other threads, I have 16GB total so didn't have that problem).

Hopefully this works for others.

The Same issues here on 2019 21.5" iMac, basically unusable from being so slow. Went back to prior the Security Update 2020-005,and all speedy again, So no doubt something really wrong in that update.

Interesting enough, my 2ghz MacBook Pro (late 2013) 8GB ram running High Sierra apparently ran the same security update and is running just fine. Clearly the issue is specific to the Mojave platform. Either way - I turned off the security updates as well on my Pro. Yes i know HS is old, but it's stable... and still runs my non-subscription CS suite which I spent big $ on.