For a time now I can't sort my wishlist anymore.
Cheapskate as I am I always sort it to discount but it doesn't work anymore.
Anyone else has this problem?

Discounted is a filter that in theory only shows items on sale. It still works for me. It may take a while after discounts go into effect until that filter realizes those items are on sale. Meaning if it's currently filtering out items with discounts for you, that's "normal" in the sense that it's one more broken thing on the site that no one intends to fix.

There's no way to sort by discount unless you're using a user script that provides that feature. You can sort by price using Dev0_NZ's bookmarklet (that's just a bookmark, but it affects the page you're on instead of loading a different site).