Using automatic setting but getting wrong timezone (missing 30 minutes) Malaysia timezone supposed to be GMT +8:00

But in my macbook (OS 10.13.5) it displays GMT +7:30 (note the last picture, bottom right), 30 minutes was missing, how can i fix this? 

Note: I tried to set it manually via select the location /closest city, it still giving me GMT +7:30

It is giving me the wrong time display on some of the website now. For example, 9:00am become 8:30am
Wow. That looks like a bug that Apple could verify and fix if you filed one. If you’re a developer, use the bug reporter. If not, calling AppleCare and asking them to help you set up the proper time zone, and if they fail, pointing them to this excellent documentation of how you sure look to me did everything correctly. 

Worst case, they explain the fix and you can post an answer here for all to learn.