Unexpected<hr> line appear when having scrollbar vertically (when height exceed 100%) - css

Question

how the title says the problem is with a line that can be seen in the next image:
If I remove the table, let's say to not have scrollbar vertically, the line also dissapear:
What I tried:
To see If html, body, div root (I use react) use height 100% but not.
To see with inspect element if that line is a hr or an element that can be removed, it's not
The only one solution seems to remove padding left-right to override the line or I don't know.
React HTML code:
return (
<React.Fragment>
<Navbar/>
<section className="container__ide">
<div className="container__settings">
<Tooltip title={'Schimbarea marimii textului pentru editorul text'} placement="left">
<Select
value={codeFontSize}
onChange={handleChangeFontSize}
MenuProps={{
anchorOrigin: {
vertical: "bottom",
horizontal: "left"
},
transformOrigin: {
vertical: "top",
horizontal: "left"
},
getContentAnchorEl: null
}}
>
{
selectFontSizeOptions.map((fontSize) => {
return <MenuItem key={fontSize} value={fontSize}>{fontSize} px</MenuItem>
})
}
</Select>
</Tooltip>
<Button>
<FaBug/>
</Button>
</div>
<div className="container__problem">
<div
className="container__statement"
>
<div className="container__top__statement">
<span>
Descriere
</span>
</div>
<div className="container__inner__statement">
</div>
</div>
<div
className="container__code"
>
<div className="container__top__code">
<span>
Solutie
</span>
<button>
Rulare cod
</button>
</div>
<div className="container__inner__code">
<Editor
height="300px"
defaultLanguage="sql"
defaultValue="// some comment"
theme="my-theme"
fontSize="20px"
onMount={handleEditorOnMount}
/>
</div>
</div>
</div>
<div className="container__result">
<MaterialTable
columns={[
{ title: 'Adı', field: 'name' },
{ title: 'Soyadı', field: 'surname' },
{ title: 'Doğum Yılı', field: 'birthYear', type: 'numeric' },
{ title: 'Doğum Yeri', field: 'birthCity', lookup: { 34: 'İstanbul', 63: 'Şanlıurfa' } }
]}
data={[
{ name: 'Mehmet', surname: 'Baran', birthYear: 1987, birthCity: 34 },
{ name: 'Mehmet', surname: 'Baran', birthYear: 1988, birthCity: 42 },
{ name: 'Mehmet', surname: 'Baran', birthYear: 1989, birthCity: 63 },
{ name: 'Mehmet', surname: 'Baran', birthYear: 1989, birthCity: 63 }
]}
title="Demo Title"
icons={tableIcons}
/>
</div>
<div className="container__comments">
<button>Adauga comentariu</button>
</div>
</section>
</React.Fragment>
)