General ⇒ Weird behaviour of \chapter.

[ppel123]

Hi everyone,
I am writing a text in latex and I am using chapters.
Everything works ok except from the chapter box.

Annotation 2020-05-30 133047.png (6.58 KiB) Viewed 2239 times

As you can see in the image above there is a line in the right side of the box that shouldn't be there.
Is this a common problem or I am missing something here?

Thanks in advance.

[Ijon Tichy]

The standard classes do not produce such a box, so you have to add a minimal working example to make the problem reproducible.