I experienced the same issue with the optimization results showing different (more) profits than the actual single tests and different drawdown, sharpe ratio and all the other values.
For me the problem was starting the optimization on a Saturday, when the markets are closed and it looks like my broker is feeding different tick values into MT5 over the weekend. Once the market opened I reoptimized and then the single test are showing the same profits and values as the optimization list.
I don't know why the tick data is different though, maybe someone has more knowledge and can shed some light on this issue..
J