I'm using the Hulu basic account, seems like that all of the videos are missing the 4K resolution now.
Checking...
Wilson
Wilson.Wang
Still related to the new manifest... no h265 on most plans, therefore no 4K.
However, I did notice the same thing, ads seem to start up just before a download options window starts, thus effectively breaking the process (maybe). Even on an ad-free plan, they usually have an intro.