Light sources not creating light

Randomly this occurred.

It is fixed by replacing the affected torches, but this is NOT a rendering or client-side issue. All server members see the same effect, and even hostile mob spawns occurred inside buildings that were previously lit up.

Obviously this is problematic and screwed a lot of farms, villages, homes, etc. and a server reset did NOT fix the issue.

I know "optimize world" may be the correct solution on singleplayer, but as this is a multiplayer server, that is not an option.

(scoreboard blurred)