I have identified a pattern with my niche site that dipped in traffic April 28th. My main KW is unchanged (serp) and my main long tail Kws that are on page 1 also remain unchanged. However my longtails that are on page 2 are fluctuating from page 2 to page 4 and beyond, not hourly fluctuation but by the day apparently.
Obviously I have lost traffic for those KWs - BUT I also lost traffic for very long phrases that come naturally without targeting. I thought it was over yesterday because I had one of my best days but around 8-9PM EST (last night) traffic again dipped and remains very low until this very minute. This disturbance is all on Google, maybe even some kind of automatic "traffic throttling." I have no idea.