Photos and videos disappearing when trying to AirDrop a video on iPhone

One minute I’m trying to download and airdrop a video Next minute it disappeared along with half of photos and videos. I got a new phone a month ago at the apple store and they transferred my photos and everything to the new phone but some did not for some reason. I tried to airdrop the video to the new phone but it deleted in front of my eyes along with over 1000 other photos/videos. The video I was trying to send had a exclamation mark at the bottom so the video was downloading to airdrop but it disappeared before it could prepare to send. My phone has been backed up and my icloud has been on but when i access my icloud photos on my pc, it’s empty. icloud.com shows that both phones were backed up but I don’t know how to access the information (more specifically the photos/videos) that were backed up. I really need urgent help bc some photos are of my father who passed and if i can’t recover them I don’t have any pictures of him.

[Re-Titled by Moderator]

Original Title: Photos deleting by themselves. One minute I’m trying to download and airdrop a video Next minute it disappeared along with half of photos and videos.