Issue is observed when post is written with aid of
text formatting(for example some programming code) and the width of the post depends on the width of the text, no line wrapping applied to it. And when you open discussion of the given 'wide' post, left part of it will be moved under contacts list pane
Telegram Desktop version 3.7.3
...text with line width more than 120+ chars ...
Telegram Desktop 3.7.3, Z390 AORUS PRO, Windows 10