With the latest version a couple of months ago, my kelp farm broke. The water stream at the top was broken allowing the kelp to just float at the top of the farm and not move to the hopper line in the back (see video). 

Now, after fixing the water system, I broke all the kelp, replanted it incase the age of the kelp was broken, and after AFKing all night the several freshly planted kelp never grew beyond 1 tall. 

See the video for an example of all the plants stuck at 1 tall. 

Edit for reference, when this farm works properly, the output should equal just over 10 furnaces to keep pace. Now it only ignites 3 of them at one time.

https://www.youtube.com/watch?v=j97o1PZZrkw&feature=youtu.be

Thanks,