So I bought an enchanted necklace that had stamina regeneration and was able to disenchant it and now I can enchant necklaces, boots, and armor with stamina regeneration. But when I saw the ring in the store with stamina regeneration I bought it and tried to disenchant it, but it will not let me. Does anyone know the reason? Or is this a bug?

Bump.....This is the only forum where a bump actually helps.

If I'm reading this correctly, by the time you purchased the ring you already had learned the stamina regeneration enchant from disenchanting an enchanted necklace. Once you know how to make a particular enchantment the game protects you from needlessly disenchanting another item with the same enchantment (in this case, the ring). Since you already know how to enchant an item with stamina regeneration, you can't learn how to do it again.

The game will list the ring as grey text instead of white in the disenchant menu. Now, in some cases some items aren't listed at all (despite having an enchantment). And I have no idea why that happens.

Cause this time enchantments are limited to only a few items so you can't enchant everything with the same effect and get too uber of a stat like 1000% magic regain.

If you go to the enchantment table and first select an effect like stamina regeneration, then go to the items tab, it will show you which items can be enchanted with it and the ones that can't will be grayed out.

^ to add to that, the game feels free to spawn loot that doesn't abide by the same restrictions, which is why you managed to find the ring despite it being a disallowed property.

This seems to be another of Bethesda's OB mod swipes. There were several mods in OB that enhanced magic, but nearly all of them restricted enchanting in some way (to reduce exploitables).