cursed earth stops working

[Dalienx]

As the title says, i just noticed today that my cursed earth is no longer spawning anything, its plenty dark enough, there is no lights at all in it.
ive got a magnum torch down to prevent other mobs spawning and it was working perfectly yesterday

 

[karmacopper]

Same issue on my home server. Issue has persisted for some time, since at least MC 1.10. Restarting my server resolves it for another 12 hours or so.