miner stats and sia mining pool are showing different hash rates

[neo.the.one]

Hello guys,
I've tested my miner two weeks ago and miner stats and "SiaMining" stats for my miner, were showing same hash rate but now, my miner shows 4TH/s while "SiaMining" shows ~700GH/s.
I'm new to mining. can anyone help me to find the problem?