Can web event eggs hatch duplicates?

A repeat is a normal result here, not a broken one. The pool you are hatching from during the pre-launch "Time to Aniimo!" event is small: Susuta, Celestis, Fentuft, Nimbi and Emberpup, each with a normal form and a sparkling one. Every normal form sits at a 14% hatch rate and every sparkling form at 6%. Those rates stay where they are no matter what you have already pulled, so the same creature coming up twice is ordinary, and one of the five refusing to show at all is just as ordinary.

Sparkling forms are on that same table, which means a duplicate and a shiny are not opposites. A hatched event character can arrive as either. The Pre-Launch Collector event behaves the same way, so duplicate copies of Aniimo are something to expect across the whole pre-launch run rather than a quirk of one egg. Joining also has you select an Aniimo to twine with, which is its own step and separate from what you hatch afterwards.

Getting what you hatch onto your account

Duplicates or not, none of it reaches you unless the login matches. Web event rewards are only granted when you log into the game with the identical email or phone number you used to pre-register, so that it lines up with the official game account. Pre-register with one address and play on another and the whole haul stays stranded. Check that before you spend time hatching, not after.

Prismana eggs are a different thing

If you have seen Prismana eggs mentioned alongside the event ones, they are not the same draw. A Prismana egg has the potential to yield a perfect Aniimo, which is a separate outcome from the normal and sparkling forms on the web event table.

Not settled: What a duplicate is actually good for once you claim it, whether it stacks into something or simply sits in your collection, is not settled before launch.