With your source code build, please open each blueprint and click compile to check if any error or warning messages appear. Please also open the water material to see if there are any warning messages when you click apply. If there are no warning messages, then please click build in the editor and try again.
If the problem persists, please send me the log from building from source and the Output Log from running the game (after trying to use Buoyancy) as text files via email to [EMAIL=“therealtheokoles@gmail.com”]therealtheokoles@gmail.com.