The update states:
"macOS Mojave 10.14.6 Supplemental Update –– Restart Required
The macOS Mojave 10.14.6 Supplemental Update fixes an issue that may prevent certain Macs from waking from sleep properly.
For information on the security content of Apple software updates, please visit this website: https://support.apple.com/kb/HT201222"
According to AppleInsider, “The original version of macOS 10.14.6 was released July 22. That sought to fix graphics glitches when waking a Mac, and it may be that Apple caught exceptions to its work in later testing. The software also made various other bug fixes and closed security vulnerabilities.”