Union with constrained type variable doesn't narrow in negative branch of type predicate

[saschaB91]

⏯ Playground Link

https://www.typescriptlang.org/play?#code/LAKAxgNghgzjAEAVApjALgYWnAPIgfPAN6jxnxoCeADsgOYCuUATgCYAUAblBAFzwMAdgGtBAewDuggJT9uEeAEsEiYqXIbmyNA2aCKzBsgDc6sgF8z8AGZd+ghgFsARsmaz4nMYtbFLIDQALOyQPLx8-K2shMC4eflUAH3gHFzcw718SAI1yRWt4djRA5QA6KlpGFg55aWk1HNzc4rLg2tNGpvItHT0Orvh-AZaYUtt2q39-UEhYFVRMbBgAJjx4ZAAPNGRBVgQAEShtwmyNCvomNji+ARFxKTCeJRUGgZ7dfTRDE0mokNTXO45JlIp02gkMhEiENyNFBLF5Al4MkAelgVCrBp8oURuUaBdqtc6q8BuRcW0eNJ+qSyO8+pjyDCmrjxpTqRZQOYgA

Issue Type: Bug

This error is only shown when using the TypeScript-Server not when compiling code.
When using an generic class with a method as type guard, it will only be validated correctly if you do not extend the generic type.
The first class is ok but the second shows an error on "this.f(val)" even though nothing changed

class TestClass<T> {
    typeguard(val: unknown): val is T {
        return true;
    }
    f(v: number): void {}
    h(v: T): void {}
    func(val: T | number): void {
        if (this.typeguard(val)) {
            this.h(val);
            return;
        }
        this.f(val);
    }
}

class TestClass2<T extends Date> {
    typeguard(val: unknown): val is T {
        return true;
    }
    f(v: number): void {}
    h(v: T): void {}
    func(val: T | number): void {
        if (this.typeguard(val)) {
            this.h(val);
            return;
        }
        this.f(val);
    }
}

[MartinJohns]

This error is only shown when using the TypeScript-Server not when compiling code.

This is not true. The error is shown when compiling just fine.

This is possibly a duplicate of #42185.

[andrewbranch]

Looks like a regression between 4.2 and 4.3