This is going to throw an exception. You try to execute an external method in the query that is send to the database.
Solve this by swapping the select and tolist. The ToList will trigger the execution of the query so the select will then be executed in c# and not the database:
return context.Feedbacks
.Include("Answer")
.Include("Question")
.Include("User")
.Where(f => f.Answer.Id == answerId)
.ToList();
.Select(f => ConvertEntities.FeedbackEntityToFeedback(f))