Currently whenever I have a fixed element (such as a header) and I want it to change width with the frame it is contained in, I first have to deselect the “fixed when scrolling” option, change the anchors and then re-enable the fixed option. Before, when that option was still in the design tab, that wasn’t a big issue, however now that the option has been moved to the prototype tab it has gotten quite annoying in my humble opinion:
I would, however, much prefer, if it was possible to do this without having to disable the “fixed-element” option in the first place.