Small Ekko bug.

So, if you proc your passive, Ekko gets a new running animation to go with that bonus MS. However, the animation doesn't end like it used to, and will keep playing until you stop moving. This same animation also pops up at random times during the game when it's not supposed to.

Though, I assume this is under the same lines as Jayce's hammer bug, and is entirely irrelevant and warrants no attention or fix, since it doesn't have any impact to your income potential.