It seems to be there is an issue when bonemealing kelp in the latest update. Now sometimes bonemealing kelp will work and other it won't and if used in a machine of some kind it will then lock up the machine and will no long ever grow again.
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Kelp seems to have a limit to how many times you can grow it with bonemeal before it stops responding. If you break and replant then you can grow it with bonemeal again. The limit in my testing is a randomly generated number roughly between 30 and 70. This behavior is discussed in the comments to MCPE-57330 and may be caused by the same bug that causes natural growth to stop, but it is not clear to me that bonemeal fueled growth should be limited even if limiting natural growth is intended behavior (perhaps as a fix to MCPE-42575).
can confirm also an issue on PC