In all the years I've been using KM, it has been extremely rare for an update to break something I'm using. Having said that, my general approach on updating any/all software is to do so only when I have a compelling reason to update. For what it is worth, I'm running Keyboard Maestro 9.0.6 on macOS 10.14.6 (Mojave) and I've not seen any issues.
So, take a look at the changes in KM 9.0.6, and decide if there is anything you really need to have. If not, then wait a month or so to see if there are any new bug reports.