What errors do Find and Marshal create? (Find does not return an error but it sets the Error field of the DB struct. Marshal does return an error as the second return value. It is always a good idea to check errors.)
And how did you change the User model? How did it look like when it was still working?
What I noticed is that the DeletedAt field appears to be a pointer to time.Time in the GORM docs. (For whatever reason.) Maybe that’s the problem here.