I know that stone monster eggs are illegal for greifing reasons but if you can do /spawner silverfish isn't that the same thing? Just it is more expensive to buy. I discovered this out when I was trying to make a zoo I did /spawner silverfish and it worked. Then a silverfish disappeared. I broke the block it was standing on and a silverfish popped out.
If /spawner silverfish is enabled then yes this is an issue and needs to be disabled. I tested this but didnt have the right conditions i think for the silverfish to come out but i could change spawners to silverfish...
To my knowledge, I don't believe me it works, the only existing silverfish spawner I know of belongs to Tcorn. If it's re-enabled, then it should be disabled again. Support.
I've tried it and it doesn't work for me. If it does work for other people it has to be disabled. ~Support~