Regardless of how you stretch your properties widget horizontally, the names get truncated the same way, even though there’s enough space to display the entire name.
The only way to fix this appears to be to delete the name, and re-paste it after the widget has been stretched horizontally
Addendum: seems like this issue is when you update the properties widget while the horizontal sizing is too small to fit certain attribute names, until you select something new or use the mentioned fix, it will always appear truncated to starting horizontal size