TypeScript Heisenbug driving me crazy: Excluding types with control statements

I simplified an error I was getting to a base case that sometimes reproduces on the TypeScript Playground, but usually it needs to be poked to be reproduced. It fails every time for me locally when running tsc.

type Result = {
  success: true,
  value: string,
} | {
  success: false,
  error: string,
};

const x = {success: true, value: 'hello'} as Result;
if (!x.success) {
  console.log(x.error);
}

TS Playground link

If you don't see an error on TypeScript Playground, click [TS Config] > and change Target. It doesn't seem to matter what I change it to. Change it to "ES2017" or "ES2019". This seems to trigger the error for me.

Questions:

(1) Is there something wrong with the approach in the code or should TypeScript be handling it?

(2) Is there a decent workaround (short of casting directly everywhere)?

TypeScript does not appear to be properly narrowing based off of the ! operator. If you do a direct comparison against the value from your union, it works (playground link):

type Result = {
  success: true,
  value: string,
} | {
  success: false,
  error: string,
};

const x = {success: true, value: 'hello'} as Result;
if (x.success === false) {
  console.log(x.error);
}

This is surprising to me, and, based on the inconsistent results, it may be worth filing a TypeScript repo issue.