So, I have a 980ti that gives me a hashrate of a little over 21 MHz/s when running in benchmark mode. But once I start actual mining using Nanopool, it drops to ~14 MHz/s, which is roughly a 33% drop. Now, I know that one should expect a certain drop in performance (e.g. 1% pool fee +1% miner fee), but a drop of 33% is too much!

Any reasons for that?