This bug has existed for as long as I could remember, and despite claims of being fixed (see: https://forums.kleientertainment.com/klei-bug-tracker/ds-shipwrecked/unable-to-hammer-down-corals-r7755/ and: https://forums.kleientertainment.com/klei-bug-tracker/ds-shipwrecked/home-sea-home-cant-hammer-coral-reefs-to-get-coral-larva-r7870/ ), it most certainly persists, and is borderline gamebreaking, causing hammering structures such as Ballphin Palaces and empty Coral Reefs to be extremely arduous, nearly impossible, and seemingly random whether or not the game lets you. People have literally been complaining about this bug since the ability to hammer those structures was added in the Home Sea Home and it still has not been fixed despite claims of it being so.
Here's a video for example:
Steps to Reproduce
Attempt to hammer a Ballphin Palace or empty Coral Reef.
This issue has not been confirmed by a developer yet.