Hi there.
I had a weird moment today. I was doing an echo, there was about a zillion monsters on the screen, and the game crashed. Okay, no big deal. Lots was going on. So I restarted, and when I came back to finish the same echo, nothing was taking any damage.
I have since restarted again, and got through the echo just fine and everything is back to normal. However, I did notice that the monsters in the echo were different then the ones that weren’t originally taking any damage.
Here is a screenshot of which echo / timeline I was on:
Here is a video of it happening:
Hope this helps.