Just tried the same macro (without Safe Boot) on my old MacBook Pro, also configured with an "ABC" keyboard. There it works fine!
The problem with this new machine is that it is configured via MDM by IT (instead of manually by me) and I'm restricted in what I can do (plus they installed a lot of software I'd rather not have on my machine - like a virus scanner that slows down my builds, making the new machine no faster than the 4 years old one...)
It is not at all implausible that they have some sort of key logging software or other event monitoring process that is messing up the event queue and interfering with the simulated keystrokes.
Actually, that is a thought, fire up Terminal, turn on Secure Keyboard Entry:
That will act as if you are in a password field, which will block applications from seeing the event queue. It will stop Keyboard Maestro’s Typed String trigger, but hot keys still work. So you a hot key triggered macro to type your text in there. See if that changes anything. It probably wont, but if it did, it would definitely point the finder at some software messing around with the event queue.