Photos randomly not saving to camera roll from Lock Screen

Help! I attended an event yesterday and took tons of photos. Most from the Lock Screen camera icon-like usual. When I clicked the thumbnail after, I could see photo no problem. But then when I unlocked phone and opened the camera roll app, the photo was gone. This happened a bunch within a few hours. However, it did not happen to all the photos, so some saved and other didn’t. This was an important event and I really wanted these photos. The signal at the event was terrible so I don’t know if that’s the reason? I also have close to full storage, but still a few GB remain. I’ve freed up more space and the photos haven’t reappeared. I restarted phone and synced to iCloud and google photos and no luck with missing photos. It’s so random and has never happened before and this was so important. Please, if anyone knows anything, I’d appreciate it. Are my photos just gone? Did they never truly save? Or are they somewhere?