Yes, sadly the Accessibility API has a nasty habit of simply ignoring part or all the request to change the window. Apparently there are apps that can make this worse or better by turning on or off an undocumented accessibility parameter.
As it is, Keyboard Maestro already executes the Accessibility requests multiple times when making the changes.
One thing to try is to simply add a Repeat action around the Manipulate a Window action (and maybe a small Pause as well) and repeat the action 3 times and see if that improves reliability.