hi,
Since last night lately my hash rate here dropped from 7~9 Th/s to 2~4 Th/s..
why is this happening?
my cgminer status shows more than 7 Th/s as usual
Could be a plethora of issues as you'll find on many pages throughout.
Depends on what equipment you have first of all. I'm assuming you have maybe 2 S7's or something? If you have an asic it could be your controller, hash boards, power supply, cables, fan, heat, etc.
Would definitely need more info than that if you're looking to get any sort of a solid direction.
I'm using an Avalon 741.
Tested with slushpool gives me scoring hash rate of 7.xx Th/s after an hour which is the normal value.