Bug is identical across both server and single player modes, which is why this is a single ticket. Please do not resolve this issue because it is not two separate tickets; these issues are one and the same. Look at pictures to see how the issues are the same.

I have experienced two instances server side, with one occurring during 1.14.2 and one occurring today as of the new update. The initial issue is quite similar to the second; a traditional mob farm I completed, even with the space completely sealed and blocking the sun with opaque blocks, appeared fully lit by the sun with light levels of 15 and 14. Slabs on the roof were replaced, block material was replaced, lighting updates with torches and water was attempted, but nothing could make the room dark. Interestingly, a room built on top of this was dark. Connecting the two rooms, however, continued the light up above into the dark ceiling of the initial taller room. Unfortunately, I have no pictures of this, but I have a similar issue which I do have screenshots of. A space was constructed for both a spawner and collection room, and was fine once completed. After re-logging into the server, however, one of the two chunks the space overlapped was lit while the other was dark. Mobs only spawned in the dark chunk, but both chunks should have been completely dark. The collection room, which should have contained both light and dark blocks, became totally lit as well, with all blocks in the collection room and partially spawner area (single chunk) at light level 15 Updating the lighting of the chunks caused the darker one to become somewhat brighter.

I noticed the other issue on a redstone ready preset on single player. A room is constructed with redstone lamps and stained glass below. Once the redstone lamps are activated and then deactivated, two neighboring chunks do not update simultaneously. One chunk updates to dark, while the bordering remains completely lit as if the lamps were still active. Note that all lamps are in fact disabled when this occurs, the lighting should not be present yet the game treats it as though it is. The screenshots depict this issue with more depth. Note that re-loading the save temporarily fixes the issue, but once the lamps are activated and de-activated again the same issue occurs in the same manner.