Hysteroscopy - first one showed a polyp, second one didn't. What's going on and where has it gone?

Hi, recently had ultra sound in uterus, was told I had thickening of womb 10 mm. Was then referred for hysteroscopy, womb was fine but had anterior polyp 1.5 cm. Doctor was trying to remove this but I was in a lot of pain. Then referred me for 2nd hysteroscopy under general anaesthetic to remove polyp. Results were, he could not see any polyp but did biopsy and said my endometrial cavity was deeper than expected. What is going on, have had no symptoms of any kind, the womb issues were found incidentally, I was sent for ultrasound for cystocele issues. The first doctor showed me the image of the polyp, where has it gone?

Thank you for reading my rant!