Apple has recently made the additional update 10.14.6 update available for macOS Mojave users.
A notable change is that Safari 14 is back after it was removed because it caused some issues for some. The security update 2020-005 in September appeared to add issues, including various error messages and delays.
The Safari 14 version is reported to stop working for some as well. Addition 10.14.6 fixes the issues related to Safari 14 and the Mojave 2020-005 update.
If you are one of those affected by Safari 14 or the 2020-005 security update, it is best to get the additional update as soon as possible. Go to the macOS System Preferences app, then go to the Software Update menu and click the ̵
Restart and test Safari 14 and see if there are still any delays or performance issues.