Blocks from Add-ons don't work, at all.

Ever since Beta 1.16.0.57, all of my downloaded add-ons that add blocks, don't work. And no, the creators of the add-ons aren't at fault, because whether the add-on was updated in Beta 1.16.0.56 or updated for Beta 1.16.0.59, they don't work. First the problem was the blocks didn't show up in the Creative Inventory, but could still be obtained using /give or a crafting table. Now, the block ids don't even exist