Macintosh Lagging on one client when bossing

I joined a 12 man HT run on my Mac with ONE client and the lag was absolutely unbearable. I would get periods of lag where my screen would be frozen for 1-2 mins. straight. Then it would be fine for 20 seconds and then freeze again. I attached a picture of the CPU % that was being used on the run.

When I "get info" on the MapleStory client, there is one client that is "size: 331,827 bytes (348 KB on disk)" and another that is "size:1,124 bytes (4 KB disk)" not sure if that makes a difference..?