It's the number of threads. You kind of just have to play around with it until you optimize it currently. I'm running multiple rigs, some max out at 2 threads per core, others at 3 or 4 threads per core, so it's highly dependent on hardware.
As far as mining, solo mining is all probability. If you're contributing 1% of the network hashrate, then you have a 1% chance of mining each block. Given 100 blocks, there's a ~63% chance that you'd mine at least one of them, but that's also a pretty good chance that you might get nothing. Even after 300 blocks, there's still a ~5% probability of mining nothing, so it's not unreasonable that streaks like this would happen occasionally. And obviously the odds are worse the lower your hashrate is relative to the total network hashrate.
The mining pool is currently in testing, which will remove a lot of the randomness from the mining process.