Since iOS11, there appears to be an intentional change in how words are wrapped within an UILabel
. Word wrapping mechanism was adjusted so as to make your multiline text wrapped with enhanced proportion. If you have a long text consisting of short words standing consecutively, it is likely that your text will be wrapped avoiding orphaned words, i.e. more than one word is about to be wrapped onto the next line. If the finishing word is long enough, then there might be no need to wrap extra words, because proportion may appear justified.
Example:
1.

Both words are wrapped, even though there's a room for one 'test' on the first line.
2.

Only the longest word is wrapped, because enough space is already occupied on the second line with it.
As of now, unfortunately, you are unlikely to influence it, since no additional properties were introduced to manage this behavior.
Workaround
There's a hack which can help in certain circumstances. You can replace whitespace with a non-breaking space (U+00A0). This way two consecutive words are treated as one which may cheat wrapping mechanism.