In a nutshell, your pH is too high. You didn't cook the curds enough or press hard enough. The curds sticking together badly is a dead give away that the pH hasn't dropped enough at hoop up. Compounding that you soaked in a room temperature brine after only 6 hours in the press. This pretty much arrested any further lactic acid production. Curd is hardest at 5.6-5.8 pH, once you start going higher and lower than that it looses body quickly.