So this has Been happening a lot but every time i ult 
as 
the chronobreaks removing the death mark now its not intended to remove debuffs and this is a huge disadvantage into an already hard match up just seeing if anyone else is having this problem. I've even tested it and chronobreak removes it in a custom game although the ability doesn't remove debuffs.
Three things are happening here:
Now, if Ekko is mid dash during 1, 2, or 3, the Death Mark should not trigger and should be removed. If Ekko completes his dash between 2 and 3, the ult should not be removed.
Much like Fiora's parry or Fizz's trollpole, certain abilities--when timed properly--can prevent Death Mark from being applied in the first place. They also can dodge the detonation.
You may test it further: apply Death Mark to Ekko, then have him ult away. If Death Mark is removed, go ahead and send the ticket in. If it is not removed, then the Ekko is just utilizing his mechanical advantage over Zed.
It briefly makes him untargetable (like Zhonyas); is it possible that the delayed damage triggered while he was untargetable?
