Some signs (banners, chests, skulls) are randomly flashing. It's like light changes only for that signs (...) .
it depends on my postion and direction (maybe only other chunks).
I hope the video describes the bug well.
I cant reproduce that for other worlds, but it happens again after a restart for this world.

https://www.youtube.com/watch?v=5SYxlojQKEc

Steps to reproduce:

• Place some signs, banners, chests, skulls
• Place an item spawner

  /setblock ~ ~ ~ minecraft:mob_spawner 0 replace {SpawnData:{id:Item,Item:{id:"minecraft:iron_ore"}}}

Code analysis by marcono1234 is found here