Macintosh Client "Screen Freeze" on mid Zakum run

Hi everyone,

I just had an unfortunate and sad experience not long ago. During the zakum run 2nd body suddenly screen freeze on the client. Firstly i thought it's my connection issue, but after waiting for roughly 1 minutes the client still freeze therefore i ALT + TAB switch to my main screen and open Firefox, the internet is working fine. The client screen freeze for more than 10 minutes, i can even switch back and forth into the client but it stay the same. So i took some screenshots. I try give most information as possible and here's my specs listed as below.

Summary:
- MapleLegends client run on full screen during zakum run
- No any application were running except MapleLegends Mac client
- client can't be close by click on the 'x' icon or right-click quit from the dock
- client only can be force quit from top left apple icon
- client screen freeze for 10 minutes
- no experiencing any screen freeze before, eg: GM event, GM buffs in FM, All kinds of PQ, lvling

Specs:
Macbook Pro 13' Early 2011
macOS High Sierra v10.13.6
2.3Ghz Intel Core i5 Sandy Bridge
Intel HD Graphics 3000 512MB
2 x 4GB DDR3 1333Mhz Corsair Apple Certified
480GB Kingston UV400 2.5' SATA SDD

Attached screen freeze screenshot: