I have seen something similar to this issue recently and it was isolated to the environment and user id being used. For example, it worked on 2 or 3 user ids used on a specific server but had no issues on previous environments whatsoever.
The selector looks rights to me, however since you are using Attach Browser, part of the selector that calls the browser and window is hidden. This looks like a bug, but you could get around this potentially by changing to an Attach Window (instead of Attach Browser) or using the full selector in the Type Into activity. Using UiExplorer will give you the full selector. But, I will suggest that you always use partials inside Attach activities to avoid sustainability headaches in the future, so you might try changing to Attach Window over Attach Browser.
I don’t know if your issue is related to what I’m seeing, but thought I would share.