Finished disc 3. Disc 4 doesn’t load up. The game freezes and the website freezes and crashes as well.
Something similar happened to me while troubleshooting. FireFox browser froze after waiting about 2 or 3 minutes for it to load. I chose to wait and then the flashing pause icon appeared and the disc loaded without any further issues.
Please try another browser (FireFox, Chrome, Edge etc) and let it do its thing until the browser responds again and the pause icon appears at the top of the game window.
Issue resolved. I saved at the save point in game and reset the game to bring up the ps1 startup screen. Loaded the game and had no issue when it came time to switch to disc 4.