As many have said, jewelers may not have solid experience with pearls. I am a GIA Graduate Gemologist with a Pearls Diploma, but it's years of seeing all kinds of pearls, looking into drill holes, examining damage and various signs of nacre alteration that qualify me to weigh in on pearls. If these people told you the pearl was fake, then they are not competent to judge pearls. At the same time, they could be very competent with other gemstones.
Your closeup photos are awesome. It's not often I can judge anything with certainty from a photo. Acid testing is helpful, but not always definitive, as you have found. I am impressed at the lengths to which you are willing to go to solve your dilemma. Please take care of yourself. Hugs ♡