See attached. The first image is what I see now. Setting that slide-out panel to have a z-index of 4 (instead of 3) addresses the bug (my last attachment shows me having manually changed the value to 4, which results in the correct second image). Pretty sure this broke in the last few days (possibly today).

Due to this bug, you can't interact correctly with the Activity slide-out. E.g. clicking the 3 dots does nothing, and clicking the x does nothing, because you aren't actually clicking them, you are clicking the navbar behind it.