lost video files

I was building a 1080X1080 social media client video and edited for 2-3 hours. The video, including all the uploaded content are missing from the file. This has happened so many times, I cannot justify using Adobe Express anymore. I watch all the negative comments with the new launch and I now completely understand the frustration. I probably could have finished the video in less than an hour if the entire system would not freeze up. Please advise.