In my Minecraft server, I have placed many torches all over a hill that contains a village. Every so often some of the torches stop giving off any light, and thus mobs spawn, confirming lack of light. I had to update the block next to each torch to get the light to come back. Does not seem to be affected per chunk, some lights can go off on levels above or below others.

The 18w50a world being copied into 19w02a server folder? Any help appreciated.

Edit: I updated Java version and still no result. Also tried single player and the same bug persists.