Q1: What is the reason why the miner sometimes becomes offline after I choose smart mining?
There are two reasons for being offline: 1) it is a brief situation after switching to smart mining; 2) The miner will become offline after not being active for 1200 seconds.
If it is the first reason, even if the miner becomes offline for a short period of time during the coin switch, the hashrate is still valid and will not be affected.
Q2: What kind of profit gap will make BTC/BCH smart mining switch?
1) If you are mining BTC, it will switch to BCH mining when the BCH profit is 2% higher than BTC.
2) If you are mining BCH, it will switch to BTC mining when BCH profit < (1+0.5%) BTC profit.
Q3: How long is the switch be made?
The switch will be made after a certain amount of profit difference, not immediately.