I was also mining on my private network for 30+ minutes and got 0 too.

I was also trying to figure out what's happening and found this:

https://github.com/ethereum/go-ethereum/blob/fe6cf00f480aa6347b8d55079cbe6c473482ea27/miner/miner.go#L142

It looks like the function's name is either misleading or we fall into the race case (bug).

I was also mining on my private network for 30+ minutes and got 0 too.

I was also trying to figure out what's happening and found this:

https://github.com/ethereum/go-ethereum/blob/fe6cf00f480aa6347b8d55079cbe6c473482ea27/miner/miner.go#L142

It looks like the function's name is either misleading or we fall into the race case (bug).