What specifically is not working? Toggling the accessibility permissions (System Preferences, Security & Privacy, Privacy, Accessibility) for Keyboard Maestro and Keyboard Maestro Engine off and then on again is generally required if you upgrade to Mojave with Keyboard Maestro already installed.
Also, simulated keystrokes that are intended to trigger hot keys in the system or other applications do not work in Mojave unless they are letters (optionally with modifiers). Simulated arrow keys or function keys do not trigger hot keys due to bugs in Mojave. This may be fixed in a future version of Mojave, or I may find a workaround in the future. In the mean time you may be able to adjust your hot keys to to use letters instead of arrows or function keys, and then they can be simulated from Keyboard Maestro.
Other than those there does not appear to be any systemic issues with Mojave.
Reinstalling Keyboard Maestro is unlikely to ever fix pretty much any issue. Installing a previous version is more likely to cause problems than solve anything.