Jayce's transition to Hammer stance from Cannon stance freezes for a split second.
It's almost like a framedrop, but as an avid Jayce main this is really distracting when playing and wasn't present last patch. I made a video about it but it doesn't do it justice. You're better off playing Jayce and seeing for yourself. Present on All skins: Classic, Forsaken, Full metal, and Debonair.
Other Jayce mains I have talked to are also saying they are having this issue so it's not just me. Hope this gets fixed asap! :)
Here is the link to the video. Look for the animation lag when I switch to Hammer stance from Cannon stance. https://www.youtube.com/watch?v=N0Zkhy6CqXQ&feature=youtu.be