Apple appears to have withdrawn the latest macOS Mojave security update (2020-005), which was released on September 24 with the macOS Catalina 10.15.7 update. Apple also removed Safari 14 for macOS Mojave from the update. As reported bymedia, both the Mojave security update and the Safari 14 update have caused problems for users who are still running macOS Mojave.
MacOS Mojave users who installed the update experienced memory problems, slow startup times and Finder Caton, a large number of system.log issues, and crashes when trying to use the Transfer Assistant. Complaints about the update began shortly after its release, but Apple did not withdraw the update until yesterday.
Those who have downloaded the Mojave security update or installed Safari 14 should be quickly fixed as updated software to resolve known errors. Restoring a Time Machine backup, reinstalling macOS Mojave, or installing macOS Catalina also appears to have successfully resolved the issue.
Update: Apple has released a supplemental update to Mojave that may address these issues.