Is this a known bug?

Hello there. Today, I was logging into my forum from my mobile phone but I saw a broken view.

I’m not that sure this really is a bug but this seems a bit weird.

Details:
Device : Apple iPhone 7 Plus
Flarum version : Beta 8.1
Tested both in here and my website.

What's wrong with this view?

Shouldn't the forum be aligned to center?