Javascript Event Source Error: {isTrusted: true} when connecting to Mercure

I have Angular on Front – End,
I have a very weird issue:
I am connecting to a Mercure – server events with EventSource in Javascript.
In case of an error for example when I simulate wrong authorization or whatever, the only thing that I receive via browser is:
{isTrusted: true}

I have red this blog: https://blog.sentry.io/what-is-script-error/
And according to the blog and other sources the issue is caused by Browser it is a Script Error.

But I tried catching the error in try catch blog,

I setup the headers according to that article.

This is how the error is handled.
How I can get some normal error format?

    this.eventSource.onerror = (error: ErrorEvent): void => {
      console.log(error);
      if (attempts === 0) {
        this._logger
          .sendToRemote$({
            id: traceId,
            log_level: 'ERROR',
            log_message: `Mercure connection dropped, after ${EVENT_SOURCE_RECONNECT_ATTEMPTS} failed attempts`,
            BODY: JSON.stringify({ message: error.message, fileName: error.filename, lineNumber: error.lineno }),
            STEP: 'ERROR',
            traceId,
            context_data: {
              sessionUid
            }
          })
          .pipe(take(1))
          .subscribe();
      }

      if (attempts > 0) {
        setTimeout(() => {
          this.startEventSource(attempts - 1);
        }, 2000);
      }
      throw error;
    };