Originally Posted by Baertram
The fix was easy and I think the problem was that there are no child controls to resize to, so the attribute was just "too much" or "not needed".
Not quite. Label's cannot be marked as resizeToFitDescendants anymore. In fact they never should have been allowing it, because they already do their own resize to fit logic, so it's competing intentions. But now they also use the same scaffolding under the hood to achieve the behavior, so marking a label resizeToFitDescendants is both wrong and can break the label. It doesn't matter whether or not it has children or how many.
TL;DR: You should never have done it, doing it now is even worse than before, and thus there's now an explicit warning about it.