Mordekaiser FPS drop

Since patch 5.18 I've been getting large FPS drops whenever a Mordekaiser appears on screen. The first 10-15 minutes of the game are okay and then all of a sudden anytime Mordekaiser appears the FPS drops from a solid 60 down to around 30-40. As soon as he leaves the screen everything is okay. Has anyone discovered a fix for this issue yet, and if so would they be kind enough to share that information with everyone having this issue?