About the portal glitch, I found one thing that causes it.
When you finish the game, you will always restart as Sora. However the last boss is fought as Riku. The game doesn't Drop Riku after the credits, so when you load your game again, the game will think you're still playing as Riku, while you're controlling Sora instead.
Fixing it should be obvious if you know the above. Drop to Riku so he gets Sora's portals, finish the game, and Sora will get his portals again.
When you finish the game, you will always restart as Sora. However the last boss is fought as Riku. The game doesn't Drop Riku after the credits, so when you load your game again, the game will think you're still playing as Riku, while you're controlling Sora instead.
Fixing it should be obvious if you know the above. Drop to Riku so he gets Sora's portals, finish the game, and Sora will get his portals again.