There is two reasons why this can happen:
1: The Bitcoin network difficulty increased. This leads to less mining returns per day. And vice versa for difficulty decreases.
2: The price of Bitcoin vs USD decreased. This leads to a higher Bitcoin deduction because the maintenance fee is fixed in USD but deducted from the payout in BTC. And vice versa if BTC price increases.
Example for 2:
if BTC price is 1,000 USD, then 1 USD equals 0.001 BTC
if BTC price is 2,500 USD, then 1 USD equals 0.0004 BTC
3. The luck that our technicians have with the selected pools we are mining in also affects the payouts.
Please take all three into account when looking at your payouts.
If you think neither of above is the reason for your changed payouts, please submit a ticket.