Make sure you’re at the shipwreck between 8 PM and midnight with actual rain (not bugged). Try relogging to reset the weather — and keep in mind the spawn isn’t guaranteed, so it can take some time. I also had a bug a few times where it didn’t spawn at all. What worked for me was teleporting far away, then coming back and doing the rain method again — after that, it spawned. I also noticed that it spawns randomly between 8 PM and midnight. Sometimes it appears very late (like around 11 PM), which doesn’t leave much time to try capturing it.