Type narrowing (null check) doesn't work if before instanceof

[yftachman]

TypeScript Version: 3.7.5 && 3.8.0-beta

Search Terms: instanceof, null check, type narrowing

Code

class A {
  constructor(public stringOrUndefined: string | undefined) {

  }
}
class B {
  constructor(public str: string) {

  }
}

const a = new A("123");

// Compiles
if (a.stringOrUndefined) {
  new B(a.stringOrUndefined);
}

// Doesn't compile
if (a.stringOrUndefined && a instanceof A) {
  new B(a.stringOrUndefined)
}

Expected behavior:
If i check an inner property undefined and then verify the type, i would expect typescript to know it is already not undefnied
Actual behavior:
instanceof "resets" the null

Playground Link:
Playground Link

Related Issues:
N\A

Notes
This is a bigger problem if my null check is not on the same if as the instance of, for example:

if (a.stringOrUndefined) {
  if (a instanceof A) {
    new B(a.stringOrUndefined)
  } else {
    // Other code that also involves a.stringOrUndefined
  }
}

As here I cannot reorder the ifs