Skylight falloff breaks after time

I built a carrot and potato farm that relies on a block update to break the carrot or potato block when the light level is 7 or less and the block receives an update.  After running the farm for a while on my multiplayer server, eventually the sky lighting will break and be a constant 15 (instead of 6 or so since it's covered by a solid roof).  This sky light value of 15 applies at any time, even at night when the block light value should override the sky light value.  Therefore, the planted crops will never break when the block receives an update.  Even breaking all light sources in and around the chunk (jack o lanterns, torches, etc.) will not fix the issue.  I also tried building another roof above those that already existed and I extended the roof of each level into the surrounding chunks, but the sky lighting shows as 15 through most of the area under the roof (although it shows as 14 and even 13 in just a couple of blocks).  The light value is visually correct when the jack o lanterns and torches are broken, but a sky light of 15 shows no matter how many roofs are placed above them.

I created the world in 19w09a and tried opening it in 19w12a and 19w12b but it did not fix the issue.  I have not experimented in earlier snapshots or releases.

The blocks in question are:
1896 67 -2744 and 1896 67 -2745 (On the bottom level of the farm)

Which show:
Client Light: 15 (15 sky, 6 block)
Server Light (15 sky, 6 block)

They showed this prior to breaking:
Client Light:  6 (6 sky, 6 block)
Server Light: (6 sky, 6 block)

And:
1896 71 -2744 and 1896 71 -2745 (On the top level of the farm)

Which show:
Client Light:  15 (15 sky, 7 block)
Server Light: (15 sky, 7 block)

They showed this prior to breaking:
Client Light:  7 (6 sky, 7 block)
Server Light: (6 sky, 7 block)

World download of world before lighting was broken:
https://drive.google.com/open?id=1t_LuijDZEo-RyHPXbhUIsPmPkzWCNvmC

World download of world after lighting was broken:
https://drive.google.com/open?id=1DTXzpnIpOg1zL3EgfbkFYgXnjJOBYANE