I noticed some unnecessary horizontal rules being rendered at the bottom of twts in the conversation view lately with yarnd’s new design change. They can be seen at least when not being logged in. Not sure if it is the same experience with an active user session. I reckon there will be fork buttons then, so in that case they would be fine, indeed.
In fact, these lines are implemented as border-top CSS properties of twt-nav-classed <nav> containers. But the <nav>s are empty, so I would expect them not being there in the first place. Empty navigation doesn’t make much sense to me.
In any case, keep up the good work! :-)