@Adam58,
Have you viewed the video that former member / 2020 ST Owner
@jmerco made available (made before FORD did a "buy back" on his ST), showing how his brakes fail?
Perhaps it will help you replicate it for the FORD service writer?!
Of course, we all know about replicating a problem for our mechanic works - but still.
The worry in all this would be the one time someone else drives your ST, or, the one day you are transitioning from a stressful environment or situation into your EX and thus you let your guard down...
As you wrote, although you don't drive it too much, it has done it once/again since getting it back from the Dealership - which means it's still an issue.
Here's the link to jmerco's video:
IMG_0246.m4v