To add an argument of type In/Out, define the same argument both before and after the name of the entry point method.
For example, you have a coded automation that takes an initial loan amount (loanAmount) and an interest rate (interestRate) as input and then calculates the updated loan amount after applying the interest rate and returns it. Also, it returns an argument stating the type of financial need that this loan amount would require.
Check out the code snippet below:
public (double loanAmount, string financialNeed) Execute (double interestRate, double loanAmount)
I cannot reproduce the issue, it loaded the arguments for me without issue. Maybe its already been fixed in a later release of Studio, can you share more details of your studio version and dependencies?