My ADU appraisal was very low

[Cesar Perini]

I have a 2b 1b house in bellflower CA. I extended it to a 3b 2b and built a 3b 2b ADU behind it. Now I own a 3b 2b house with an ADU that has 3b 2b. I'm refinancing the house now and my appraiser used comps of a SFH with only 3b 2b and NO ADU. That brought my appraisal value down a lot!! To me a home that doesn't have 6 beds and 4 baths isn't comparable to my house at all! Am I wrong for thinking this? Anyways, I disputed the original appraisal and the 2nd appraisal said they can't find comps with ADUs and can't use a comp that's a duplex so I have to keep the original appraisal. Any advise here or is this the way ADUs are appraised?