Please check the graph on my screenshot again. it shows hashrate per hour, not per second, so it should normaly be around 4.5-5.0 Gh/s for 5x1080 ti per hour.
+ as you can see I have 2 more rigs and their hashrate is constant.
Sorry Nemo for dropping in but need to explain this to this gentleman...
Hashrefinery is now placing a stratum server reset daily... I have emailed him several times about this and a fix has been made...