I think this is a correct behavior.

$ cat -n multiline_assignment.py 
     1  x = 1
     2  y = 2
     3  z = [
     4      x,
     5      y,
     6  ]

$ ./python -m trace --trace multiline_assignment.py

In 3.7 the line with the assignment is missed:

 --- modulename: multiline_assignment, funcname: <module>
multiline_assignment.py(1): x = 1
multiline_assignment.py(2): y = 2
multiline_assignment.py(4):     x,
multiline_assignment.py(5):     y,

In 3.8:

 --- modulename: multiline_assignment, funcname: <module>
multiline_assignment.py(1): x = 1
multiline_assignment.py(2): y = 2
multiline_assignment.py(4):     x,
multiline_assignment.py(5):     y,
multiline_assignment.py(3): z = [