For example the Greymoor Add-on for ESO:
Two items with the same name, referring to the same thing. You can buy one, the other one is just there for... what, exactly?
If these two items refer to the same thing, why are there two of it? If these two refer to slightly different things, why do they have the same name?
@LokiBrot I've noticed this too, and it made purchasing the Greymoor expansion quite a chore. Two entries for that expansion is inconvenient, but other add-ons apparently can't be purchased individually at all with the version of ESO included with the Pro subscription (Elsweyr, Summerset, etc.).
I'm not sure if there's a reason for this or if it's a simple mistake in the store listing, but I'd encourage you to join me in using the in-app Feedback option to let the team know about the confusion.