Both for word-wrap: break-word; and overflow-wrap: break-word; CSS properties i have a premature breaking problem at the very end like in this case. Besides, with longer strings I even witnessed this problem manifest itself in different forms like not breaking at all at the expected end of the line or self inventing a wider or narrower width for the remaining of the lines.

The question is, when you have a very long string why does overflow-wrap: break-word; "break" at certain unexpected places..?

var str = Array.from({length:65366}, _ => ~~(Math.random()*9) + 1)
               .reduce((s,c) => s + c, ""),
    blk = document.getElementById("block");

blk.textContent = str;

#block{
    margin : 0 auto;
    font-family: monospace;
    width: 90vw;
    overflow-wrap: break-word;
}

<p id="block"></p>

Note: This problem doesn't seem to exist in Firefox but in Chrome and Edge i can see it. Also while scrolling down you may notice that the right margin changes.