Amumu ult circle bug

I encountered the bug shown in the during a ranked game which would show the amumu ult (circle) every 2-3 secs at dragon pit. I don't know how it occurred or how it can be reproduced may through using amumu ult in drake pit but even in that situation this is the first time I have encountered the bug with an amumu in my games. link of the ranked game just for reference

PS: I have two monitors thats why you can see the game playing on the left and the screenshot of few seconds before in paint on the right.