BRZ HID ballast problem?
 

My left side high beam stopped working.

I've changed the bulb and checked all the fuses multiple times.

Could a ballast malfunction cause this problem?

Low bean works perfectly fine.

it's not a ballast problem. your high beam solenoid might be stuck, or a bad fuse. there is no separate bulb or voltage for high beams. once you turn on the high beams, it actuates a solenoid inside the projector that lowers a cut-off plate, revealing the entire output of your bulb. low beams have that cut-off plate up, blocking half of the output of the bulb (hence why there is the flat cut-off)

so, how do I check for bad solenoid?

and what other fuse should i check?

i replaced the bulb already and checked fuse and even replaced proper fuse.

I remember someone mentioning the DRL relay controlling the high beams as well so that would be a good place to start. try having someone stand with their ear next to the projector while you turn on/off the high beams and see if they can hear the click of the solenoid activating.