I have faced this also before. The screen is filled with garbage ( both HW and PE) and the audio interrupt seems not to work (plays the same block on and on on HW). The reason is that I use print("test") command in a rooms.py file. Sometimes the print command in the “wrong” place causes this(!). Without the print command it works 
Here is the project sources:
Matti (90).zip (111.9 KB)
Edit: looks like tilemap drawing is what get corrupted.