The type(t) is not M check should not narrow the type of t, since a subclass can have the metaclass:

from typing import Type

class M(type):
    pass

class C: pass

class D(C, metaclass=M): pass

def f(t: Type[C]) -> None:
    if type(t) is not M:
        return
    reveal_type(t)  # <nothing>

f(D)

I'd expect that the revealed type to be Type[C], not <nothing>. The latter can cause false positives.

This is a regression from mypy 0.812.