with 42.2, the trick to open the easter egg sketchpad to obscure the map layer eliminated the Slacker stuttering/glitching issue for me (MCU1 / AP1).
FYI I recently updated to 48.12.1, and I now notice that every time I get ouf of the car (ie park/lock the car for even just a minute), when I get back into the car the map is no long covered by the sketchpad! I have to manually set everything back the way I wanted (sketchpad covering map, music on bottom, rear camera above), each time I go to drive the car.
I'm pretty certain this is new behaviour and that with 42.2 the sketchpad previously stayed put unless you did something with the UI that got rid of it (e.g. bring up nav or close the sketchpad yourself). The stuttering in Slacker in 48.12.1 is less frequent than before but still exists, and the sketchpad workaround still seems to work - BUT it's very annoying that the sketchpad closes for no reason now and you have to reposition everything each time.