skelaton and zombie spawner wont spawn

[Sander__XD]

when i got the savanna island i get the skelaton spawners and i made a new grinder for it and now my skelaton and zombies wont spawn

 

[iiDangerYT]

try making on other island

 

[Patsman]

It takes 5-10 minutes for mobs to spawn after you have placed the spawner. I haven't heard of this bug yet, so like iiDanger said, try a different island. If it doesn't work, then report it Here. Cubecraft will try to fix it.