The release notes of Mojave (https://support.apple.com/en-gb/HT209149) are reasonably comprehensive, if you jsut need a list of what's changed, but contained within the 10.14.4 notes is the line:
Resolves Wi-Fi connection issues that may occur after upgrading to macOS Mojave.
This is pretty vague. As a sysadmin, I'd like to know specifics about the issue and what the fix has done to resolve it. Does Apple publish more detailed bug tracking or deep dives in to their bug fixes and/or known issues?