This is a long-standing bug–or at least shortcoming–in Axure. When a widget is set to “Fit to Text Width” it only works in the editor, not dynamically. When a widget is in a repeater the editor seems to treat each row as if it had different widgets, but in the browser it is definitely “repeated duplicates” --so the widget will be the same width in all rows, regardless of whether “Fit to Text Width” is set. In other words, it would need to be dynamically resized as the repeater loads, and that doesn’t happen. Technically, this is the way it is documented to work, but realistically nobody expects this or wants it to behave this way.
Here are a few threads and workaround solutions for this topic: