Under the settings in the main menu (click on your SF logo on the top left) and go to the menu that has the game history button at the bottom. To the right of that, there will be a button that either says link or unlink. If it says unlink, click that button. A window will pop making sure you want to do it.
Then, go to theshow.com. Click on the account link. Click on The Show account (not the PS account that gives you the market, inventory, and such). Unlink Twitch there. Go to Twitch and log in. Go to the link settings and make sure it’s unlinked. If not, unlink it.
Then, go back to the first step and start linking it back up. For good measure, you may want to quit the game before relinking and close your browser to reset things. Whether that’s necessary or not, I don’t know. I did it just to be safe. I think I even reboot my console, but I’m OCD.
After your done relinking, give things some time. Oh, and make sure you claim your packs in Twitch. You don’t have do do this at the same time as linking, but it has to be done for them to show up in your inventory.
Hope this helps.