Why a price mismatch between MAM Master and Investor orders is possible
MAM is an account type that is based on copier.
So positions just get copied to investment accounts from master account according to one of 7 formulas: allocation methods. Allocation method is set on investor by a Master.
That means that positions on master account are independent from positions of investment accounts. And they are opened by different orders and deals with tiny time delay.
Execution Prices for investor and master can be same, but as well can be different due to market activity and liquidity.
Investors can get both negative and positive slippages.