Upgrade to 2.1 breaks existing .net core EF logic

I have 2 objects with a FK relationship between them. All of this logic worked fine when i was using .net core 2, but broke when i upgraded to 2.1

public class Parent
{
     [Key()]
     public Guid ParentGUID {get;set;}
     public string SomeValue {get;set;}
     [ForeignKey("ReferenceTypeGUID")]
     public ReferenceType ReferenceTypeObject {get;set;}
}
public class ReferenceType
{
     [Key()]
     public Guid ReferenceTypeGUID{get;set;}
     public string SomeOtherValue {get;set;}
     public virtual ICollection<Parent> ParentGU { get; set; }
}

and then in my dbcontext i have

 modelBuilder.Entity<ReferenceType>(entity =>
        {
            entity.HasKey(e => e.ReferenceTypeGUID);

                entity.HasMany(c => c.ParentGU)
                    .WithOne(e => e.ReferenceTypeObject)
                    .HasForeignKey(f => f.ParentGUID)
                    .OnDelete(DeleteBehavior.ClientSetNull);
});

Now in my original code, i didn't have the HasForeignKey line, and i got the following error:

cannot target the primary key because it is not compatible

adding that line fixed that issue, but now i'm getting

Operand type clash: int is incompatible with uniqueidentifier

for some reason, EF is assuming that the database type should be int instead of uniqueidentifier, even though the object is declared as a GUID. how do i fix this issue?