It seems like kraken and bittrex are using something called "average" last price when we ask for last price on their API: in this condition, if you set sell level too low (say at 1%) and we are not fast enough to get the "last price" it can easily and fastly drop at 0.25% for example, because it is not a real last price but an "average".
So, until i will not get an answer from the ticket support i open on their desks, please set kraken and bittrex GAIN at least 2% (or higher if your trading style is fine with it).
Thanks!