So I believe this is a bug i encountered while messing around in a custom game with Ekko. After I purchased a rapid fire cannon, I began to proc RFC with my e ability. I found that if the damage from RFC is enough to kill a target (I did it on a minion), you would not dash to that target afterwards. So basically The RFC damage was granting you the killing blow and in turn you would not dash to that target, as you would remain at your original position. I tested it a few times and it stayed true with jungle monsters, caster minions, melee minions, and cannon minions. Please up vote so rito can see this.
It seems to be a problem with kircheis shard so shiv may be affected by it as well
The same thing happens with shiv. I get to proc it and does the damage to the nearby enemies but it does not make me dash.
Step 1: Buy static shiv, RFC, or the shard
Step 2: Use your E ability while the item passive is charged to 100
Step 3: Use your E ability on a minion, monster, etc. when its health is low enough to just be killed by the ability passive