Hi Emre,
This sounds like a problem with the broker or their server. Slippage maybe. Or it could be a problem with the auto trading. I’d suggest making sure your auto trading is enabled, you see the smiley face (or hat in the case of MT5) in the top right hand corner. If all settings are confirmed as correct, run a backtest. You will see trades that should have opened. Then contact the prop firm and enquire with them why the trades didn’t open, when they clearly should have according to the backtest. Also, check the journal for any errors.
Cheers,
Ilan