Getting this error now. When using this code. The model (also is x) is of type UserDetailModel, the sub property User is of type EmployeeDTO. This worked just fine until version 3.17.2, I've test in 3.17.1 and it still works.
@f.FormGroup().DisplayFor(x => x.User.FirstName)
The model item passed into the dictionary is of type 'UserDetailModel', but this dictionary requires a model item of type 'EmployeeDTO'.