Ultrasound of my kidneys provides different results, please advise?

Hello in 2010 I had an ultrasound after seeing a nephrologist. My right kidney measured 10×3.6 cm and my left 9.8×3.8 cm…the notation said slight increased echogenicity of both kidneys in prominent pyramids. And the impression was suggesting medical renal disease…now the nephrologist said that I had significant scarring in both kidneys. Which baffled him because my blood work was great. Now a few days ago after getting an ultrasound of my kidneys there was nothing it was all normal. And while I’m thankful I’m confused and no one seems to be able to tell me why this can occur. Can you tell me why this might be the case?

Age: 29
Female
Medications: Methotrexate, prednisone, gabapentin
General Information: I was diagnosed with fibromyalgia in 2017 and my Rheumatologist thinks I may have RA or sarcoidosis.