brightening and dimming light traveling across the sky in a large arc then disappearing.

First off let me state that I am an amateur astrophotographer / astronomer. I know the difference between things such as the ISS, meteors, satellites, planes and iridium flares. On the night of May 15th I had set up my telescope to take some pictures of the lunar eclipse. I was taking pictures every 10 minutes or so to see the progression of the lunar eclipse. Soon after the moon was is the earth's shadow the stars became much more visible. That is when I saw what at first I thought was the space station since that is about how bright it appeared. As I watched it I noticed that it was cycling in brightness (approximately 2-3 seconds from maximum brightness to minimum brightness). At first I thought it could be due to very small and light clouds coming across the sky that night but it was not random and continued with a repeating cycling pattern. Also it did not cross the sky in a straight line, it did a large arc from almost straight above me then to the east and then traveled back in a SE direction. The speed did not seem consistent either (it would speed up and almost seem to be stationary at times). When it got to a point in the eastern sky it brightened one last time and immediately disappeared. I tried to get the telescope on it but I don't think I changed the settings on my camera correctly to capture it (it was set up for the eclipse). I ran in the house fast to grab my phone to see if I could get a video of it. I began recording it but could not see the object on the screen so I stopped recording. Later I checked my phone and I must have just caught it on video for maybe a second. Due to it being a screen grab of the video (or my camera moving) it appeared as a streak. You could see on the paused video that is was appeared to be a square object with lights on the corners and maybe one light in the middle of each side. I went to bed that night thinking when I woke up that I hear about it in the morning on Facebook or somewhere on the internet due to the fact that it was during the lunar eclipse and a lot of people would have been looking in the sky at this exact time, but no, nothing. I also thought maybe it was an prank with a drone but I don't think it could travel the distance it did in the short 2-3 minutes it was visible. I kept trying to explain it away but could not.