Skylight appearing in an enclosed box on my server

There is a 10 block radius in my underwater farm that has random skylight in it. I have a roof above my farm, which should have solved this issue ages ago, however, I gave this issue the benefit of the doubt and decided to enclose my farm thinking the light is coming from somewhere else.. but NOPE. This bug is reducing the efficiency of my farm and I hope it gets resolved very soon :/. Also to add the top half of my farm has a light level of 0 whilst the midsection has a light level of 15 and the bottom half ranges from 8-12.