We updated how discounts work. To summarize you can no longer use a single discount for Products AND Plans AND Events. Now, Products, Plans and Events each have their own set of discounts.
The fallout from this is you may need to clean up / do maintenance to your discount pages. You can now find the discounts specific to each type under the main menu.
Going to each Discount Type page, you may see all your old discounts under the Legacy Discounts list. These discounts will still work if you have assigned them to people on Plans/Products/Events, however, you wont be able to edit them or assign them to anyone else.
Using the 3 dots contextual menu you can 'reclassify' them which will lock them into one type and then you will be able to use them again for future members. You probably want to take a few minutes now and clean this up.