[MC-149518] Skylight appearing under blocks

Notice

This issue is fixed starting the release of 1.14.3. But if you had this issue on a existing world, you will need to purge the light data in order to fix your map.

On singleplayer: from the worlds menu, select your world, click Edit, Optimize World; then be sure to check the box Erase Cache Data before proceeding.
On server: run your map (only) once by appending these arguments at the end of your java startup command: --forceUpgrade --eraseCache. If you don't have shell access to the host system, either contact your host provider, or download your world, paste it inside your singleplayer save folder, proceed with the singleplayer steps, and finally re-upload your map.

Do not confirm this issue for new version nor open any new ticket until you have tried those steps.

Original Description

Came across a random patch of daylight at the bottom of a ravine, with no source above. Checking light levels, it shows 15 from the sky when standing in it, and 14 when completely enclosed in dirt. Light colour seems to match daylight cycle.