The workaround I have found for this is to put back the word-break: break-word in the text-break class, like it was in the previous versions;
Confirmed:

Most investigation shows this works with block level elements, but when flexbox is introduced, it falls apart. See https://codepen.io/emdeoh/pen/dyYjwoO?editors=1100.
Cross referencing some things...
/cc @MartijnCuppens
By default, flex items won鈥檛 shrink below their minimum content size. Setting min-width: 0 on concerned flex items fix the text break. See https://codepen.io/florianlacreuse/pen/ZEbMGda (FWIW)
Oh yeah, didn't think about that at all. Do we ship this as a fix, or tell folks to use min-width: 0 (and possibly provide a utility for that)? Feels like we do both: ship this and add some docs around this behavior.
Adding the min-width will be quite hard to implement with our utility API I guess
@MartijnCuppens You okay then with shipping an update to bring back word-break: break-word on the utility and a mention about this flexbox issue in our docs? And, likely for v4 and v5?
Same issue here (MacOS / Google Chrome 81.0.4044.138 / Bootstrap 4.5)
An element with class text-break no longer works properly if it is placed inside an element with the class d-flex.
min-width:0 fix the problem for now
@mdo @MartijnCuppens Be careful, as I said in this issue word-break: break-word is deprecated, just for the record.
@nicolomonili Thanks, see the anwser about the minimum content size behavior on flex items.
The problem is also present with tables / td, but in this case the problem persists even adding min-width:0. Try to add class="text-break"on a <td> with a long text.
Ok with 4.4 https://getbootstrap.com/docs/4.4/content/tables/#responsive-tables

Not ok with 4.5 https://getbootstrap.com/docs/4.5/content/tables/#responsive-tables

In this case table-layout: fixed; makes things work fine. But yeah less than ideal. I will be OK with any decision, even if we need to go back to word-break property.
Looking at this Codepen I made a couple weeks ago again, it seems like a browser bug or unintentional behavior that word-break: word-wrap would have different behavior than word-wrap: break-word/overflow-wrap: break-word with flex containers. While the former is deprecated, it fixes some weird behaviors, so I'm in favor of bringing it back.
@mdo @XhmikosR This fix was backported to v4 with without keeping word-wrap: break-word for IE and Edge Legacy (see: https://github.com/twbs/bootstrap/issues/29319)
There's no issue in v5:
.text-break {
word-wrap: break-word !important;
word-break: break-word !important;
}
But in v4 we have word-break which didn't support break-word value in IE and Edge Legacy (comment in source is wrong) and overflow-wrap which is absent in IE/Edge Legacy (it's modern replace for word-wrap):
.text-break {
word-break: break-word !important; // IE & < Edge 18
overflow-wrap: break-word !important;
}
So .text-break don't work in IE/Edge Legacy in v4 now.
I fixed it by sync .text-break in v4 with v5 and created PR for that: https://github.com/twbs/bootstrap/pull/31727
Unfortunately .text-break don't work inside flex containers in IE/Edge Legacy even with this fix.
This happens because it don't support break-word value for word-break property.
In modern browsers word-break: break-word treated as word-break: normal+overflow-wrap: anywhere (which means it work inside flex), but in IE/Edge Legacy we only have word-wrap: break-word supported which has the same effect as overflow-wrap: break-word (which didn't work inside flex).
To fix it we need to define a width for the container.
See: https://stackoverflow.com/questions/35111090/text-in-a-flex-container-doesnt-wrap-in-ie11#answer-35113633
width: 100% works both in IE and Edge Legacy,
flex-basis: 100% and flex: 1` will work only in IE11, not in Edge Legacy.
Most helpful comment
The problem is also present with tables / td, but in this case the problem persists even adding
min-width:0. Try to addclass="text-break"on a<td>with a long text.Ok with 4.4 https://getbootstrap.com/docs/4.4/content/tables/#responsive-tables

Not ok with 4.5 https://getbootstrap.com/docs/4.5/content/tables/#responsive-tables
