Having this same issue on uk ps store for last few days.
Managed somehow to download episode 2 from within the game however no luck with episode 3.
Upon searching the store only the season pass(which i own) and episodes 1,4 and 5 are visible.
Contacted sony support though no real help.
Got a reply from Telltale support instead which offered a hopeful solution quote; "We have been in contact with Playstation regarding this issue. We have requested that they make some changes to the back end of their servers to help potentially resolve this issue.We are hoping to have a response from them regarding when these changes will be implemented soon.
Thank you for your patience as we work out the problems."
Hoping for a fix real soon really enjoying the game.