Placing any underwater Plants in underwater areas you have created yourself doesn't work. For example if I made an underwater area and tried putting kelp in it or corals it won't work. This bug affects sea grass, kelp, all coral plants and all coral fans. Placing them underwater in natural sea areas is fine. Please fix
Linked issues
duplicates 1
Comments 5
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-32920.
Your additional information and observations are very useful, so if you can add them to the comments section of the parent issue it would be appreciated.
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Are you trying to place them in flowing water or source blocks?