Monster Spawners in survival mode are stuck as pigs - when they shouldn't be, i.e. in abandoned mineshafts. Nothing spawns from them. Playing survival with hard mode locked.
MC-100659
Monster Spawners stuck on pig - won't spawn anything
Resolved
Invalid
0
This was caused by opening the world in 1.8.x temporarily. Also the cause of the empty chests in your other bug report MC-100660