So lighting seems to randomly be broken. I could have sworn that this was fixed quite a long time ago, but it seems to be back worse than ever. The worst part about it this time it that it doesn't seem to be just client side, but actually server side as other people can see it and it is not fixed on relog. As well as the fact that mobs seemingly can spawn in it in the middle of the day due to the block light and sky light being both marked as 0. Example screenshots are below. 

Mumbo Jumbo recently encountered this issue as well (timestamp 9:12): https://youtu.be/3avo6rSqDZ0?t=9m12s

Another example from Mumbo Jumbo (timestamp 14:02): https://youtu.be/l6WiFXkhG4A?t=14m2s