[disastrouswerd]

Hello guys. I have a 5sp manual hyundai i30 fd 1.6crdi, 2010. One day after 3 hours of traffic , I was parking and I couldn't get it out of reverse, I turned the car off released the clutch, the clutch went up till half, and then I lifted it up with my foot and it came out of gear okay. My mechanic suspected it was the slave cylinder, and we changed that and put a new one, it was true the old one was destroyed lol. Today the same thing happened, couldn't get it out of first gear and reverse while parking after 2 hours of driving. Turned the car off and got it out of gear just fine, clutch was okay this time. I have changed gear oil 2 months ago and put the right one and very good one. Can it be the master cylinder?
 
P.S. weird thing car shifts better when cold, and worse when it's been driving for some hours.